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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Mar. 12, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	Clearside Biomedical, Inc.
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	CLSD
Document Type	10-K
Entity Central Index Key	0001539029
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		31,913,113
Entity Public Float			$ 153,311,000

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 9,224	$ 34,824
Short-term investments	28,416	48,807
Prepaid expenses	1,445	396
Other current assets	116	290
Total current assets	39,201	84,317
Property and equipment, net	885	94
Restricted cash	360	360
Other assets	47	42
Total assets	40,493	84,813
Current liabilities:
Accounts payable	5,384	2,594
Accrued liabilities	4,716	2,791
Current portion of long-term debt	3,200
Current portion of deferred rent	199	3
Other current liabilities	20	20
Total current liabilities	13,519	5,408
Long-term debt	4,809	7,586
Deferred rent	610
Deferred revenue	140	160
Total liabilities	19,078	13,154
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized and no shares issued at December 31, 2017 and 2016
Common stock, $0.001 par value; 100,000,000 shares authorized at December 31, 2017 and 2016; 25,354,651 and 24,573,033 shares issued and outstanding at December 31, 2017 and 2016, respectively	25	25
Additional paid-in capital	145,618	136,892
Accumulated deficit	(124,220)	(65,245)
Accumulated other comprehensive loss	(8)	(13)
Total stockholders’ equity	21,415	71,659
Total liabilities and stockholders’ equity	$ 40,493	$ 84,813

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares, issued	25,354,651	24,573,033
Common stock, shares outstanding	25,354,651	24,573,033

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
License and collaboration revenue	$ 345	$ 520
Operating expenses:
Research and development	49,053	19,455	$ 10,762
General and administrative	9,700	6,263	6,555
Total operating expenses	58,753	25,718	17,317
Loss from operations	(58,408)	(25,198)	(17,317)
Other expense	(567)	(684)	(322)
Net loss	$ (58,975)	$ (25,882)	$ (17,639)
Net loss per share of common stock — basic and diluted	$ (2.33)	$ (1.97)	$ (7.54)
Weighted average shares outstanding — basic and diluted	25,311,614	13,111,067	2,338,950
Net loss	$ (58,975)	$ (25,882)	$ (17,639)
Unrealized gain (loss) on available-for-sale investments	5	(13)
Comprehensive loss	$ (58,970)	$ (25,895)	$ (17,639)

Statement of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-In-Capital	Additional Paid-In-Capital Redeemable Convertible Preferred Stock	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2014	$ (19,213)		$ 2	$ 2,509		$ (21,724)
Beginning balance, shares at Dec. 31, 2014			1,816,467
Exercise of stock options	14			14
Exercise of stock options, shares			50,980
Vesting of restricted stock, shares			14,203
Issuance of common stock upon exercise of warrants	(1)		$ 1	(2)
Issuance of common stock upon exercise of warrants, Shares			777,612
Accretion of stock issuance costs	(525)			(525)
Share-based compensation expense	705			705
Net loss	(17,639)					(17,639)
Ending balance at Dec. 31, 2015	(36,659)		$ 3	2,701		(39,363)
Ending balance, shares at Dec. 31, 2015			2,659,262
Exercise of stock options	31			31
Exercise of stock options, shares			10,724
Vesting of restricted stock, shares			6,485
Issuance of common stock upon exercise of warrants	410			410
Issuance of common stock upon exercise of warrants, Shares			133,560
Issuance of common stock in initial public offering	51,377		$ 8	51,369
Issuance of common stock in initial public offering, Shares			8,148,843
Issuance of common stock in follow-on offering	33,459		$ 4	33,455
Issuance of common stock in follow-on offering, Shares			4,000,000
Conversion of preferred stock to common stock	48,198		$ 10	48,188
Conversion of preferred stock to common stock, Shares			9,614,159
Issuance of warrants to purchase common stock	308			308
Accretion of stock issuance costs		$ (884)			$ (884)
Share-based compensation expense	1,314			1,314
Net loss	(25,882)					(25,882)
Other comprehensive gain (loss)	(13)						$ (13)
Ending balance at Dec. 31, 2016	71,659		$ 25	136,892		(65,245)	(13)
Ending balance, shares at Dec. 31, 2016			24,573,033
Issuance of common shares under employee stock purchase plan	66			66
Issuance of common shares under employee stock purchase plan, shares			9,692
Exercise of stock options	239			239
Exercise of stock options, shares			171,926
Issuance of common stock in follow-on offering	5,057			5,057
Issuance of common stock in follow-on offering, Shares			600,000
Share-based compensation expense	3,364			3,364
Net loss	(58,975)					(58,975)
Other comprehensive gain (loss)	5						5
Ending balance at Dec. 31, 2017	$ 21,415		$ 25	$ 145,618		$ (124,220)	$ (8)
Ending balance, shares at Dec. 31, 2017			25,354,651

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (58,975)	$ (25,882)	$ (17,639)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	182	65	60
Share-based compensation expense	3,364	1,314	705
Non-cash interest expense	211	283	104
Accretion of debt discount	212	108	60
Change in fair value of warrant liability		156	52
Amortization and accretion on available-for-sale investments, net	(31)	(43)
Loss on sale of fixed assets			15
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(833)	(487)	(145)
Other assets	(5)	882	1,763
Accounts payable and accrued liabilities	4,715	1,424	632
Deferred revenue	(20)	(520)	500
Deferred rent	97	(9)	(9)
Net cash used in operating activities	(51,083)	(22,709)	(13,902)
Investing activities
Purchase of available-for-sale investments	(48,116)	(54,485)
Maturities of available-for-sale-investments	68,543	5,708
Change in restricted cash		(360)
Acquisition of property and equipment	(306)	(3)	(32)
Proceeds from the sale of fixed assets			4
Net cash provided by (used in) investing activities	20,121	(49,140)	(28)
Financing activities
Proceeds from follow-on offering, net of issuance costs	5,057	33,456
Proceeds from initial public offering, net of issuance costs		51,376
Proceeds from exercise of stock options	239	31	14
Proceeds from shares issued under employee stock purchase plan	66
Proceeds from issuance of long-term debt		7,857	5,976
Principal payments made on long-term debt		(6,330)
Net cash provided by financing activities	5,362	86,390	25,944
Net (decrease) increase in cash and cash equivalents	(25,600)	14,541	12,014
Cash and cash equivalents, beginning of period	34,824	20,283	8,269
Cash and cash equivalents, end of period	9,224	34,824	20,283
Supplemental disclosure
Interest paid	653	250	100
Tenant improvements paid by landlord	$ 637
Conversion of convertible preferred stock to common stock		48,198
Reclassification of deferred initial public offering costs		1,597
Issuance of warrants to purchase common stock		308
Issuance of warrant to purchase Series B preferred stock			164
Accretion of redeemable convertible preferred stock to redemption value		884	525
Unpaid initial public offering costs in accounts payable and accrued expenses		$ 507	410
Series C Preferred Stock
Financing activities
Proceeds from the issuance of Preferred Stock, net of issuance costs			$ 19,954

The Company	12 Months Ended
The Company	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company	1. The Company Clearside Biomedical, Inc. (the “Company”) is a late-stage clinical biopharmaceutical company developing first-in-class drug therapies to treat blinding diseases of the eye. The Company’s current product candidates focus on treatments for diseases affecting the retina and choroid, especially diseases associated with macular edema, and are injected into the suprachoroidal space (“SCS”) using its proprietary SCS Microinjector. Incorporated in the State of Delaware on May 26, 2011, the Company has its corporate headquarters in Alpharetta, Georgia. The Company’s activities since inception have primarily consisted of developing product and technology rights, raising capital and performing research and development activities. The Company has no current source of revenue to sustain present activities, and does not expect to generate meaningful revenue until and unless the Company receives regulatory approval of and successfully commercializes its product candidates. The Company is subject to a number of risks and uncertainties similar to those of other life science companies at a similar stage of development, including, among others, the need to obtain adequate additional financing, successful development efforts including regulatory approval of products, compliance with government regulations, successful commercialization of potential products, protection of proprietary technology and dependence on key individuals. Liquidity On June 1, 2016, the Company’s registration statement on Form S-1 relating to its initial public offering of its common stock (the “IPO”) was declared effective by the Securities and Exchange Commission (“SEC”). The IPO closed on June 7, 2016 and the Company sold 7,200,000 shares of common stock at a price to the public of $7.00 per share, for net proceeds of $45.3 million. On June 30, 2016, the underwriters of the IPO partially exercised their option to purchase additional shares, and on July 6, 2016, the Company sold 948,843 additional shares of common stock at a price to the public of $7.00 per share, for net proceeds of $6.1 million. The Company paid to the underwriters underwriting discounts and commissions of $4.0 million in connection with the IPO, including the underwriters’ exercise of their option to purchase additional shares. In addition, the Company incurred expenses of $1.6 million in connection with the IPO. Thus, the aggregate net offering proceeds to the Company, after deducting underwriting discounts and commissions and offering expenses, were $51.4 million. On December 9, 2016, the Company’s registration statement on Form S-1 relating to its follow-on public offering of its common stock was declared effective by the SEC. The follow-on public offering closed on December 14, 2016 and the Company sold 4,000,000 share of common stock at a price to the public of $9.00 per share, for net proceeds of $33.4 million. On December 30, 2016, the underwriters of the follow-on public offering exercised their option to purchase additional shares and on January 6, 2017, the Company sold 600,000 additional shares of common stock at a price to the public of $9.00 per share, for net proceeds of $5.1 million. The Company paid to the underwriters underwriting discounts and commissions of $2.5 million in connection with the follow-on public offering, including the underwriters’ exercise of their option to purchase additional shares, and incurred expenses of $0.4 million in connection with the follow-on public offering. On June 30, 2017, the Company entered into an at-the-market sales agreement with Cowen and Company LLC (“Cowen”), under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock having an aggregate offering price of up to $50.0 million through Cowen acting as its sales agent. As of the date of this report, the Company has not sold any shares of its common stock under the at-the-market facility. On March 12, 2018, the Company closed a follow-on public offering in which it sold 6,538,462 shares of common stock at a public offering price of $13.00 per share, resulting in net proceeds of $79.6 million after deducting underwriting discounts and commissions and estimated offering expenses. Prior to the IPO, the Company had funded its operations primarily through the sale of convertible preferred stock and the issuance of long-term debt, resulting in aggregate proceeds of approximately $53.9 million. Even with the completion of the IPO and the subsequent public offerings of common stock, the Company will continue to need to obtain additional financing to fund future operations, including completing the development and commercialization of its primary product candidates. The Company will need to expend substantial resources for research and development, including costs associated with the clinical testing of its product candidates. The Company will also need to obtain additional financing to conduct additional trials for the regulatory approval of its drug candidates if requested by regulatory bodies, and completing the development of any additional product candidates that might be acquired. If such products were to receive regulatory approval, the Company would need to prepare for the potential commercialization of its product candidates and fund the commercial launch of the products, if the Company decides to commercialize the products on its own. Moreover, the Company’s fixed expenses such as rent and other contractual commitments are substantial and are expected to increase in the future. The Company had cash, cash equivalents and short-term investments of $37.6 million as of December 31, 2017. In the absence of product or other revenues, the amount, timing, nature or source of which cannot be predicted, the Company’s losses will continue as it conducts its research and development activities. Until the Company can generate sufficient revenue, the Company may finance future cash needs through public or private equity offerings, license agreements, debt financings, collaborations, strategic alliances and marketing or distribution arrangements. The Company has incurred losses and negative cash flows since inception and expects operating losses and negative cash flows to continue into the foreseeable future. However, the Company is able to control spending on development activities while proceeding with a new drug application and still advancing clinical trials for key drug candidates and the Company expects that the cash on hand as of the filing date, March 16, 2018, will be sufficient to fund its operations for at least the next 12 months from that date.

Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Significant Accounting Policies

2. Significant Accounting Policies

Basis of Presentation

The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of income and expenses during the reporting periods. Significant items subject to such estimates and assumptions include the accounting for useful lives to calculate depreciation and amortization, clinical trial accruals, share-based compensation expense and income tax valuation allowance. Actual results could differ from these estimates.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment.

Property and Equipment, Net

Property and equipment is recorded at historical cost. Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets, or for leasehold improvement the lesser of the useful life or remaining lease term . Repairs and maintenance are expensed when incurred. Upon retirement or sale, the cost of the assets disposed of and the related accumulated depreciation are removed from the accounts, and any resulting gain or loss is included in the determination of net income.

Debt Discount

All debt discounts are recorded against the related debt obligation and are amortized using the effective interest rate method over the term of the underlying debt obligation and reflected in interest expense.

Fair Value Measurements

The Company records certain financial assets and liabilities at fair value in accordance with the provisions of Accounting Standards Codification (“ASC”) Topic 820, Fair Value Measurements and Disclosures, on fair value measurements. The Company’s material financial instruments at December 31, 2017 and 2016 consisted primarily of cash and cash equivalents, short-term investments and long-term debt. The fair value of cash and cash equivalents, other current assets, and accounts payable approximate their respective carrying values due to the short term nature of these instruments.

Income Taxes

Deferred tax assets or liabilities are recorded for temporary differences between financial statement and tax basis of assets and liabilities, using enacted rates in effect for the year in which the differences are expected to reverse. A valuation allowance is recorded if it is more likely than not that a deferred tax asset will not be realized. The Company has provided a full valuation allowance on its deferred tax assets, which primarily consist of cumulative net operating losses of $28.0 million for the period from May 26, 2011 (inception) to December 31, 2017. Due to its history of operating losses since inception and losses expected to be incurred in the foreseeable future, a full valuation allowance was considered necessary.

Reverse Stock Split

On May 11, 2016, the Company effected a 1-for-2.2 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s convertible preferred stock. Accordingly, all share and per share amounts for all periods presented in these financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios. The adjustment to the conversion ratio for the Series C convertible preferred stock also included an anti-dilution adjustment based on the initial public offering price of the Company’s common stock.

Research and Development Costs

Research and development costs are charged to expense as incurred and include:

•

employee-related expenses, including salaries, benefits, travel and share-based compensation expense for research and development personnel;

•

expenses incurred under agreements with contract research organizations, contract manufacturing organizations and consultants that conduct clinical and preclinical studies;

•

costs associated with nonclinical and development activities;

•

costs associated with technology and intellectual property licenses;

•

costs for the Company’s research and development facility; and

•

depreciation expense for assets used in research and development activities.

Costs for certain development activities, such as clinical studies, are recognized based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, or information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the patterns of costs incurred, and are reflected in the financial statements as prepaid or accrued liabilities No material adjustments to these estimates have been recorded in these financial statements.

Share-Based Compensation

Compensation cost related to share-based awards granted to employees is measured based on the estimated fair value of the award at the grant date. The Company estimates the fair value of stock options using a Black-Scholes option pricing model. Compensation expense for options granted to non-employees is determined as the fair value of consideration received or the fair value of the equity instruments issued, whichever is more reliably measured. The fair value of awards granted to non-employees is re-measured each period until the related service is complete. Share-based compensation costs are expensed on a straight-line basis (net of estimated forfeitures) over the relevant vesting period.

Compensation cost related to shares purchased through the Company’s employee stock purchase plan, which is considered compensatory, is based on the estimated fair value of the shares on the offering date, including consideration of the discount and the look back period. The Company estimates the fair value of the shares using a Black-Scholes option pricing model. Compensation expense is recognized over the six month withholding period prior to the purchase date.

All share-based compensation costs are recorded in general and administrative or research and development costs in the statements of operations based upon the underlying employees’ roles within the Company.

Cash Equivalents

Cash equivalents consist of short-term, highly liquid investments with an original term of three months or less at the date of purchase.

Short-Term Investments

Short-term investments are investments with original maturities of between 90 and 365 days when purchased and are comprised of certificates of deposit, commercial paper, corporate and government bonds and treasury bills. The Company classifies its short-term investments as available-for-sale securities. Short-term investments are recorded at fair value and unrealized gains and losses are recorded within accumulated other comprehensive loss until realized. In addition, the Company evaluates the short-investments with unrealized losses to determine whether such losses are other-than-temporary.

Restricted Cash

The Company is required to maintain a stand-by letter of credit as a security deposit for its facility lease in Alpharetta, Georgia. The Company’s bank requires the Company to maintain a restricted cash balance to serve as collateral for the letter of credit issued to the landlord by the bank. As of December 31, 2017, the restricted cash balance was invested in a commercial money market account.

Concentration of Credit Risk Arising From Cash Deposits in Excess of Insured Limits

The Company maintains its cash in bank deposits that at times may exceed federally insured limits. The Company has not experienced any loss in such accounts. The Company believes it is not exposed to any significant risks with respect to its cash balances.

Recent Accounting Pronouncements

Accounting Pronouncements Recently Adopted

In August 2016, Financial Accounting Standards Board (“FASB”) issued ASU 2016-15, Statement of Cash Flows Classification of Certain Cash Receipts and Cash Payments. The update addresses eight specific cash flow matters with the objective of reducing diversity in practice in how certain cash receipts and payments are classified in the statement of cash flows. The update is effective for annual periods beginning after December 15, 2017, and interim periods within the period. Early adoption is permitted. The Company adopted the standard effective January 1, 2018, and the adoption did not have a material impact on its financial statements and related disclosures.

In November 2016, the FASB issued ASU 2016-18, Restricted Cash, which addresses diversity in practice in the classification and presentation of a change in restricted cash on the statement of cash flows. The amendments in this update require that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. The Company adopted the standard effective January 1, 2018, and the adoption did not have a material impact on its financial statements and related disclosures.

Recent Accounting Pronouncements Not Yet Adopted

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers. Under ASU 2014-09, companies will be required to recognize revenue to depict the transfer of goods or services to customers in amounts that reflect the consideration (that is, payment) to which the company expects to be entitled in exchange for those goods or services. The new standard also will result in enhanced disclosures about revenue, provide guidance for transactions that were not previously addressed comprehensively (for example, service revenue and contract modifications) and modify guidance for multiple-element arrangements. In August 2015, the FASB issued ASU 2015-14, which deferred by one year the effective date of ASU 2014-09.

The Company plans to adopt the standard using the modified retrospective transition method. After evaluating its current and prior license agreements, as well as its other collaboration agreements, the Company does not expect that the adoption of ASU 2014-09 will not have a material impact on its financial statements and related disclosures.

In February 2016, the FASB issued ASU No. 2016-02, Leases (ASC 842), which requires lessees to recognize most leases on the balance sheet. This is expected to increase both reported assets and liabilities. The new lease standard does not substantially change lessor accounting. For public companies, the standard will be effective for the first interim reporting period within annual periods beginning after December 15, 2018, although early adoption is permitted. Lessees and lessors will be required to apply the new standard at the beginning of the earliest period presented in the financial statements in which they first apply the new guidance, using a modified retrospective transition method. The requirements of this standard include a significant increase in required disclosures. The Company is currently assessing the impact that adopting this new accounting standard will have on its financial statements and related disclosures.

Property and Equipment, Net

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment, Net

3. Property and Equipment, Net

Property and equipment, net consisted of the following (dollar amounts in thousands):

	Estimated Useful Lives (Years)	December31,
		2017			2016
Furniture and fixtures	5	$	303		$	69
Machinery and equipment	5		121			121
Computer equipment	3		41			27
Leasehold improvements	Lesser of useful life or remaining lease term		667			45
Total property and equipment			1,132			262
Less: Accumulated depreciation			(247	)		(168	)
Property and equipment, net		$	885		$	94

Accrued Liabilities

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Accrued Liabilities

4. Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31,
	2017		2016
Accrued research and development	$	3,360	$	1,153
Accrued bonuses		920		870
Accrued professional fees		62		410
Accrued vacation		113		72
Accrued interest payable		58		52
Accrued expense		203		234
	$	4,716	$	2,791

Long-Term Debt

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Long-Term Debt

5. Long-Term Debt

Loan and Security Agreements

In April 2015, the Company entered into a loan agreement (the “original loan agreement”) with Silicon Valley Bank (“SVB”) for borrowings up to $6.0 million, with a floating interest rate equal to the Wall Street Journal’s prime rate minus 0.50%. Under the terms of the original loan agreement, an initial tranche of $4.0 million was advanced on April 15, 2015 and an additional tranche of $2.0 million was advanced on May 15, 2015. The Company was required to pay accrued interest only for a period of 12 months from the date of each advance, followed by 30 equal monthly payments of principal and accrued interest. A final payment of $0.3 million, or 5.50% of the aggregate borrowed amount, was due at maturity of the loan in 2018 and was being accreted in long-term debt over the life of the loan. Closing costs of $24,000 were recorded against the long-term debt liability and were also being accreted over the life of the loan.

In September 2016, the Company entered into an amended and restated loan and security agreement, which was subsequently amended on October 31, 2017 (as amended, the “loan agreement”) with SVB, MidCap Funding XII Trust and MidCap Financial Trust (together, “MidCap” and collectively with SVB, the “Lenders”), which amended and restated in its entirety the Company’s original loan agreement. The loan agreement provides for new term loans of up to $15.0 million, with a floating interest rate equal to 7% plus the greater of (i) the 30-day U.S. LIBOR, reported in the Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest will accrue, or (ii) 0.50%.

Under the terms of the loan agreement, an initial tranche of $8.0 million was advanced on September 28, 2016. The Company may draw the remaining $7.0 million through March 31, 2018. The Company was required to pay accrued interest only through December 31, 2017 on the outstanding amount, followed by 30 equal payments of principal and accrued interest. The Company has the option to prepay the outstanding balance of the term loans in full, subject to a prepayment fee of 2% of the original principal amount of the aggregate term loans for any prepayment through May 31, 2020. A final payment of $0.5 million, or 6.50% of the aggregate borrowed amount, is due at maturity of the loan on June 1, 2020, or upon the prepayment of the facility or the acceleration of amounts due under the facility as a result of an event of default, and is being accreted in long-term debt over the life of the loan. Of the initial $8.0 million advanced on September 28, 2016, $5.3 million was used to repay all amounts outstanding under the original loan agreement. Closing costs incurred in the refinancing portion of the loan were recorded as expense while the financing costs for the new portion of the loan are recorded in long-term debt and being accreted over the life of the loan. Upon repayment of the original loan agreement, all remaining closing costs associated with the original loan agreement are being accreted to long-term debt over the life of the new loan.

The term loans under the loan agreement are secured by substantially all of the Company’s assets, except that the collateral does not include any of the Company’s intellectual property. However, pursuant to the terms of a negative pledge arrangement, the Company has agreed not to encumber any of its intellectual property.

Interest expense on the borrowings under the original loan agreement and the loan agreement was $653,000, $287,000 and $115,000 for the years ended December 31, 2017, 2016 and 2015, respectively. Accretion of the scheduled final payment under the original loan agreement and the loan agreement was $211,000, $283,000 and $101,000 for the years ended December 31, 2017, 2016 and 2015, respectively. Accretion of the deferred closing costs under the original loan agreement and the loan agreement was $62,000, $17,000 and $7,400 for the years ended December 31, 2017, 2016 and 2015, respectively.

As of December 31, 2017, the scheduled payments for the loan agreement, including the scheduled final payment in 2020, were as follows (in thousands):

Year Ending December 31,	Principal		Interest and Final Payment		Total
2018	$	3,200	$	476	$	3,676
2019		3,200		234		3,434
2020		1,600		545		2,145
	$	8,000	$	1,255	$	9,255

Convertible Shareholder Notes Payable	12 Months Ended
Convertible Shareholder Notes Payable	Dec. 31, 2017
Equity [Abstract]
Convertible Shareholder Notes Payable	6. Convertible Shareholder Notes Payable In April 2014, the Company authorized the sale of convertible promissory notes (the “Bridge Notes”) to its existing stockholders, including two of its executive officers and one of its directors in their individual capacities, in the aggregate principal amount of $6.0 million. In April 2014, the Company issued $3.0 million in aggregate principal amount of Bridge Notes. The outstanding notes accrued interest at a rate of 7%, with principal plus interest due upon maturity in April 2015, unless earlier converted. The Bridge Notes were convertible upon the occurrence of a qualified financing which occurred in August 2014, and accordingly the principal and interest under all of the Bridge Notes was converted automatically into an aggregate of 1,137,652 shares of Series B convertible preferred stock in connection with the financing. In connection with the issuance of the Bridge Notes, the Company also issued warrants to the lenders to purchase an aggregate of 112,802 shares of common stock at an exercise price of $0.02 per share. These warrants, which would have otherwise expired upon the closing of the IPO, were automatically net exercised for an aggregate of 112,441 shares of common stock upon the closing of the IPO.

Convertible Preferred Stock

12 Months Ended

Dec. 31, 2017

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

7. Convertible Preferred Stock

As of December 31, 2015, the Company had authorized an aggregate of 20,913,331 shares of Series A, A-1, B and C convertible preferred stock, par value $0.001 per share. Upon the closing of the Company’s IPO, all 20,839,633 shares of the Company’s convertible preferred stock that were issued and outstanding on that date were automatically converted into an aggregate of 9,614,159 shares of its common stock.

The following table summarizes the activity of convertible preferred stock (in thousands, except per share amounts):

																									Total
	Series A						Series A-1						Series B						Series C						Convertible
	Preferred Stock						Preferred Stock						Preferred Stock						Preferred Stock						Preferred
	Shares			Amount			Shares			Amount			Shares			Amount			Shares			Amount			Stock
Balance at January 1, 2016		5,198,826		$	4,086			4,356,931		$	7,900			6,009,202		$	15,372			5,274,674		$	19,956		$	47,314
Accretion of redeemable convertible preferred stock to redemption value		—			—			—			—			—			840			—			44			884
Conversion of preferred stock to common stock at closing of IPO		(5,198,826	)		(4,086	)		(4,356,931	)		(7,900	)		(6,009,202	)		(16,212	)		(5,274,674	)		(20,000	)		(48,198	)
Balance at December 31, 2016		—		$	—			—		$	—			—		$	—			—		$	—		$	—

As of December 31, 2017 and 2016, there were 10,000,000 shares of preferred stock authorized, none of which were issued and outstanding.

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2017
Equity [Abstract]
Common Stock	8. Common Stock The Company’s amended and restated certificate of incorporation authorizes the Company to issue 100,000,000 shares of $0.001 par value common stock. As of December 31, 2017 and 2016, there were 25,354,651 and 24,573,033 shares of common stock outstanding, respectively.

Stock Purchase Warrants	12 Months Ended
Stock Purchase Warrants	Dec. 31, 2017
Stock Purchase Warrants [Abstract]
Stock Purchase Warrants	9. Stock Purchase Warrants Preferred Stock Warrants During 2013, in connection with a loan agreement, the Company issued a warrant to the lender to purchase up to 16,550 shares of Series A-1 preferred stock at a price per share of $1.8132. The term of the warrant extended until 10 years from the grant date and the warrant was exercisable at any time during that 10-year period. This warrant was outstanding at December 31, 2015 and had a weighted average remaining life of 6.8 years and a fair value of $58,000. The warrant was automatically converted to a common stock warrant and was net exercised on June 6, 2016, in connection with the IPO, resulting in the issuance of 3,236 shares of common stock. In April 2015, in connection with the original loan agreement, the Company issued a warrant to the lenders to purchase up to 57,143 shares of Series B preferred stock at a price per share of $3.50. The term of the warrant extends until 10 years from the grant date and the warrant is exercisable at any time during that 10-year period. The warrant was automatically converted into a warrant to purchase 25,974 shares of common stock at an exercise price of $7.70 upon the closing of the IPO. This warrant was outstanding at December 31, 2015 and had a weighted average remaining life of 9.25 years and a fair value of $0.2 million. This warrant was net exercised on October 12, 2016, resulting in the issuance of 17,883 shares of common stock. Common Stock Warrants During 2014, in connection with the sale of convertible promissory notes in connection with a preferred stock financing, the Company issued warrants to the lenders to purchase up to an aggregate of 112,802 shares of common stock at a price per share of $0.02. These warrants were outstanding at December 31, 2015 and had a remaining life of 8.2 years. These warrants, which would have otherwise expired upon the closing of the IPO, were automatically net exercised for an aggregate of 112,441 shares of common stock upon the closing of the IPO. In September 2016, in connection with the loan agreement, the Company issued warrants to the Lenders to purchase up to 29,796 shares of common stock at a price per share of $10.74. The warrants expire in September 2026, or earlier upon the occurrence of specified mergers or acquisitions of the Company, and are immediately exercisable. The warrants were recorded in equity and had a remaining life of 8.75 years as of December 31, 2017.

Share-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

10. Share-Based Compensation

Stock Options

In January 2016, the Company’s board of directors adopted and approved the Clearside Biomedical, Inc. 2016 Equity Incentive Plan (the “2016 Plan”) which became effective on June 1, 2016. The 2016 Plan provides for the grant of share-based awards to employees, directors and consultants of the Company. The Company reserved 1,818,182 shares of common stock for issuance under the 2016 Plan. The 2016 Plan provides for the grant of incentive stock options to employees, and for the grant of nonqualified stock options, restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards and other forms of stock compensation to the Company’s employees, directors, and non-employee third parties. The number of shares of common stock reserved for issuance under the 2016 Plan will automatically increase on January 1 each year, for a period of ten years, from January 1, 2017 through January 1, 2026, by 4% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors. At December 31, 2017, under the 2016 Plan, options to purchase 2,044,400 shares of the Company’s common stock were outstanding at a weighted average price of $7.98 per share and 751,078 shares remained available for future grant. As of January 1, 2018, the number of shares of common stock that may be issued under the 2016 Plan was automatically increased by 1,014,186 shares, representing 4% of the total number of shares of common stock outstanding on December 31, 2017, increasing the number of shares of common stock available for issuance under the 2016 Plan as of that date to 1,765,264 shares.

As a result of the adoption of the 2016 Plan, no further grants may be made under the Company’s 2011 Stock Incentive Plan (the “2011 Plan”). The 2011 Plan provided for the grant of share-based awards to employees, directors and consultants of the Company. At December 31, 2017, options to purchase 1,013,713 shares of the Company’s common stock were outstanding under the 2011 Plan at a weighted average exercise price of $2.47 per share.

The Company has granted stock option awards to employees, directors and consultants. The total share-based compensation expense recognized is reflected in the statements of operations as follows (in thousands):

	Year Ended December 31,
	2017		2016		2015

Research and development	$	1,348	$	539	$	327
General and administrative		1,988		775		378
Total	$	3,336	$	1,314	$	705

Share-based compensation is accounted for in accordance with the provisions of ASC 718, Compensation-Stock Compensation. The estimated fair value of options granted is determined as of the date of grant using the Black-Scholes option pricing model. The resulting fair value is recognized ratably over the requisite service period, which is generally the vesting period of the awards.

The following table sets forth the weighted average assumptions utilized in the fair value calculation for the underlying common stock for the years ended December 31, 2017, 2016 and 2015.

	Year Ended December 31,
	2017			2016			2015

Expected term (years)		7.00			7.00			7.00
Expected stock price volatility		96.85	%		97.45	%		86.63	%
Risk-free interest rate		2.20	%		2.20	%		2.09	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

Expected term (in years): The Company utilized the guidance set forth in ASC 718 to determine the expected term of options. The Company utilized the simplified method as prescribed by ASC 718, as the Company does not have sufficient historical exercise and post-vesting termination data to provide a reasonable basis upon which to estimate the expected term of stock options granted to employees.

Risk-free interest rate: The risk-free interest rate is based on the yields of U.S. Treasury securities with maturities similar to the expected time to a possible liquidity event.

Expected dividend yield: The Company has not paid and does not anticipate paying any dividends in the foreseeable future.

Expected stock price volatility: The volatility assumption is based on the historical volatilities of the stock of several public entities that are similar to the Company, as the Company does not have sufficient historical transactions in its own shares on which to base expected volatility. A similar peer group of companies was utilized for 2017 and 2016.

Forfeitures: As of January 1, 2017, upon adopting ASU 2016-09, the Company began recording forfeitures as they occurred. In prior years, the Company had estimated its forfeiture rate to be zero for the periods presented and any expense true-ups for terminated employees have been immaterial.

The following table summarizes the activity related to stock options during the year ended December 31, 2017:

				Weighted
	Number of			Average
	Shares			Exercise Price

Options outstanding at January 1, 2017		2,243,575		$	5.78
Granted		1,127,950			6.45
Exercised		(171,926	)		1.37
Cancelled/Forfeited		(124,250	)		8.40
Options outstanding at December 31, 2017		3,075,349			6.17

Options exercisable at December 31, 2016		789,120			1.55

Options exercisable at December 31, 2017		1,114,286			3.94

The following table provides additional information about the Company’s stock options that were outstanding and exercisable at December 31, 2017 (aggregate intrinsic values in thousands):

							Weighted								Weighted
			Weighted				Average				Weighted				Average
			Average		Aggregate		Remaining				Average		Aggregate		Remaining
Exercise	Options		Exercise		Intrinsic		Contractual		Options		Exercise		Intrinsic		Contractual
Price	Outstanding		Price		Value		Life (Years)		Exercisable		Price		Value		Life (Years)

$0.02 - $0.40		465,265					5.4			465,265					5.4
$3.08 - $5.89		1,385,871					8.9			356,632					7.2
$6.16 - $8.90		1,105,921					8.9			264,161					8.2
$9.11 - $20.84		118,292						9.0		28,228					8.9
		3,075,349	$	6.17	$	5,598	8.4			1,114,286	$	3.94	$	4,180	6.7

As of December 31, 2017, the Company had $11.6 million of unrecognized compensation expense related to unvested stock options, which is expected to be recognized over a weighted average period of 3.1 years. The weighted-average fair values of all stock options granted for the years ended December 31, 2017, 2016 and 2015 was $5.25 per share, $7.89 per share and $5.72 per share, respectively. The intrinsic value is calculated as the difference between the fair market value and the exercise price per share of the stock options. The fair market value per share of common stock as of December 29, 2017 was $7.00, which was the closing sale price of the Company’s common stock on the Nasdaq Global Market on that date.

Employee Stock Purchase Plan

In January 2016, the Company’s board of directors adopted and approved the Clearside Biomedical, Inc. 2016 Employee Stock Purchase Plan (the “2016 ESPP”) which became effective on June 1, 2016. The 2016 ESPP permits employees to purchase shares of the Company’s common stock through payroll deductions up to 15% of their earnings. The Company reserved 181,818 shares of common stock for issuance under the 2016 ESPP. Additionally, the number of shares reserved for issuance under the 2016 ESPP will automatically increase for a period of ten years, from January 1, 2017 through January 1, 2026, by the lesser of (i) 1% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, (ii) 454,545 shares of common stock or (iii) a lesser number of shares as may be determined by the Company’s board of directors. As of January 1, 2018, the number of shares of common stock that may be issued under the 2016 ESPP was automatically increased by 253,546 shares, representing 1% of the total number of shares of common stock outstanding on December 31, 2017, increasing the number of shares of common stock available for issuance under the 2016 ESPP as of that date to 671,402 shares.

The first offering period for the 2016 ESPP commenced on January 1, 2017. The 2016 ESPP is considered a compensatory plan and the fair value of the discount and the look-back period are estimated using the Black-Scholes option pricing model and expense is recognized over the six month withholding period prior to the purchase date. During the year ended December 31, 2017, the Company issued 9,692 shares of common stock purchased under the 2016 ESPP, and $21,000 and $7,000 of share-based compensation expense was recorded in general and administration expense and research and development expense, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

11. Income Taxes

No provision for U.S. federal or state income taxes has been recorded as the Company has incurred net operating losses since inception. Significant components of the Company’s net deferred income tax assets consist of the following (in thousands):

	December 31,
	2017			2016			2015
Deferred tax asset (liability)
Net operating loss carryforwards	$	27,999		$	23,391		$	14,119
Non-deductible accrued expenses		248			358			230
Deferred rent		49			1			4
Deferred revenue		38			69			77
Stock compensation expense		387			101			88
Depreciation differences		(18	)		(13	)		(28	)
Federal tax credits		3,437			1,232			850
State tax credits		524			301			262
Charitable contributions		6			6			3
Valuation allowance		(32,670	)		(25,446	)		(15,605	)
Net deferred tax asset	$	—		$	—		$	—

A reconciliation of the statutory tax rates and the effective tax rates is as follows:

	Year Ended December 31,
	2017			2016			2015
U.S. federal tax rate		34.00	%		34.00	%		34.00	%
State tax rate		2.42			3.79			4.54
Permanent difference and other		(2.84	)		(1.98	)		(1.26	)
Tax credit		3.97			1.62			2.66
Valuation allowance		(12.42	)		(37.43	)		(39.94	)
Impact of federal rate change		(25.13	)		—			—
		0.00	%		0.00	%		0.00	%

In December 2017, the 2017 Tax Cuts and Jobs Act (the “2017 Tax Act”) was signed into law. The 2017 Tax Act significantly revises the U.S. corporate income tax by, among other things, lowering the statutory corporate tax rate from 34% to 21%, eliminating certain deductions, imposing a mandatory one-time tax on accumulated earnings of foreign subsidiaries, introducing new tax regimes, and changing how foreign earnings are subject to U.S. tax. The 2017 Tax Act also enhanced and extended through 2026 the option to claim accelerated depreciation deductions on qualified property. The Company has not completed its determination of the accounting implications of the 2017 Tax Act on its tax accruals. However, the Company has reasonably estimated the effects of the 2017 Tax Act and recorded provisional amounts in its financial statements as of December 31, 2017. The Company recorded a provisional tax expense of the impact of the 2017 Tax Act of approximately $14.9 million. This amount is primarily comprised of the re-measurement of federal deferred tax liabilities resulting from the permanent reduction in the U.S. statutory corporate tax rate to 21% from 34%. As the Company completes its analysis of the 2017 Tax Act, collects and prepares necessary data, and interprets any additional guidance issued by the U.S. Treasury Department, the IRS, and other standard-setting bodies, the Company may make adjustments to the provisional amounts. Those adjustments may materially impact the Company’s provision for income taxes in the period in which the adjustments are made. Based on the Company’s history of net operating losses, any benefit that is being or will be derived from the 2017 Tax Act will be offset by a full valuation allowance, as discussed further below.

Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Due to the Company’s history of operating losses, the deferred tax assets arising from the aforementioned future tax benefits are currently not likely to be realized and, accordingly, are offset by a full valuation allowance. The income tax provision varies from the expected provision determined by applying the federal statutory income tax rate to income (loss). The difference in the expected provision, as determined by applying the federal statutory income tax rate to income (loss) is primarily due to the increase in the deferred income tax valuation allowance of $7.2 million, $9.8 million and $7.0 million for the years ended December 31, 2017, 2016 and 2015, respectively, and in 2017, the impact of the federal rate change because of the 2017 Tax Act.

As of December 31, 2017, the Company had net deferred tax assets primarily related to net operating loss carryforwards of $28.0 million, which expire through 2037. Utilization of the net operating loss carryforwards and credits may be subject to a substantial annual limitation due to the ownership change limitations provided by the Internal Revenue Code of 1986, as amended, and similar state provisions. The effect of an ownership change could be an imposition of an annual limitation on the use of net operating loss carryforwards attributable to periods before the change.

The U.S. federal statute of limitations remains open for the periods from inception and forward. The Company has not been the subject of examination by the taxing authorities.

The Company has no uncertain tax positions.

Commitment and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

12. Commitments and Contingencies

Lease Commitment Summary

The Company had previously leased office space under non-cancelable operating leases which expired in March 2017.

In November 2016, the Company signed a new office lease agreement to lease approximately 20,000 square feet of office space in Alpharetta, Georgia for its corporate headquarters. The lease agreement is for a six and one-half year term with a renewal option for one additional five-year term. Rental payments are $35,145 per month subject to an increase of 3% per year. Rent expense under this lease is recognized on a straight-line basis over the term of the lease. In addition, the lease agreement requires payment of the pro-rata share of the annual operating expenses associated with the premises. The Company relocated to this new space in March 2017.

Minimum lease payments were as follows at December 31, 2017 (in thousands):

Year ending December 31,
2018	$	431
2019		444
2020		458
2021		472
2022		487
Thereafter		373
Total minimum lease payments	$	2,665

Rent expense was $214,000, $81,000 and $150,000 for the years ended December 31, 2017, 2016 and 2015, respectively.

Contract Service Providers

In the course of the Company’s normal business operations, it has agreements with contract service providers to assist in the performance of its research and development, clinical research and manufacturing. Substantially all of these contracts are on an as needed basis.

License and Collaboration Agreements	12 Months Ended
License and Collaboration Agreements	Dec. 31, 2017
License And Collaboration Agreements [Abstract]
License and Collaboration Agreements	<div> <p style="margin-top:9pt;margin-bottom:0pt;text-indent:0%;font-weight:bold;font-family:Times New Roman;font-size:10pt;font-style:normal;text-transform:none;font-variant: normal;">13. License and Collaboration Agreements</p> <p style="margin-top:6pt;margin-bottom:0pt;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;text-indent:4.54%;">In August 2014, the Company entered into a royalty-bearing license agreement with NovaMedica LLC (“NovaMedica”). Under this agreement, the Company granted to NovaMedica the right to use the Company’s intellectual property to develop and commercialize the intended products (the “Covered Products”) and to have the exclusive right to sell those products in Russia and specified adjacent territories involving the use of the corticosteroid triamcinolone acetonide as the sole active pharmaceutical ingredient for administration in the SCS. In connection with this royalty-bearing license, NovaMedica made an upfront payment to the Company of $200,000. The Company is currently developing product candidates that when completed would be subject to this license giving NovaMedica the exclusive right to then sell the products in the specified geographic territories. In mid-December 2015, the Company received positive results from the Phase 2 clinical trial relating to the product candidate and determined, based on these results, that the intellectual property could become commercially feasible. Beginning in the first quarter ended March 31, 2016, the Company began recognizing the $200,000 to revenue over the period of time to complete clinical development and commercialization of the Covered Products and the beginning of the first set of patent expirations in 2027. The Company recorded $20,000 of license revenue during each of the years ended December 31, 2017 and 2016 for this license agreement. NovaMedica is jointly owned by Rusnano MedInvest LLC (“Rusnano MedInvest”) and Domain Russia Investments Limited. RMI Investments, which beneficially owned approximately 6% of the Company’s voting securities as of December 31, 2017, is a wholly owned subsidiary of Rusnano MedInvest.</p> <p style="margin-top:12pt;margin-bottom:0pt;text-indent:4.54%;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">In April 2015, the Company entered into a license and collaboration agreement (the “Spark Agreement”) with Spark Therapeutics, Inc. (“Spark”) under which Spark could acquire the exclusive rights to license the Company’s microinjector technology and access to the SCS within the eye for development and ultimate commercialization of Spark’s gene therapy treatments to be delivered via the microinjector. In conjunction with executing the Spark Agreement, Spark made an upfront, non-refundable payment to the Company of $500,000. </p> <p style="margin-top:12pt;margin-bottom:0pt;text-indent:4.54%;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">In February 2016, the initial study was completed and Spark elected not to extend the arrangement nor license the technology which terminated the Spark Agreement in accordance with the agreement terms. During the quarter ended March 31, 2016, the Company recorded as revenue the $500,000 upfront payment as the amount was non-refundable and the Company had no further obligations under the Spark Agreement.</p> <p style="margin-bottom:0pt;margin-top:0pt;text-indent:4.17%;font-family:Times New Roman;font-size:10pt;"> </p> <p style="margin-bottom:0pt;margin-top:0pt;text-indent:4.17%;font-family:Times New Roman;font-size:10pt;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">The Company has periodically entered into other short-term collaboration agreements to evaluate the potential use of its proprietary SCS microinjector with third-party product candidates for the treatment of various diseases. Funds received from these collaboration agreements are recognized as revenue over the term of the agreement. The Company recorded $325,000 of revenue from these collaboration agreements during the year ended December 31, 2017.</p></div>

Available-for-Sale Investments

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Available-for-Sale Investments

14. Available-for-Sale Investments

The following table summarizes the Company’s available-for-sale investments as of December 31, 2017 (in thousands):

	December 31, 2017
	Amortized		Unrealized			Fair
	Cost		Loss			Value

Government bonds and agency obligations	$	11,241	$	(3	)	$	11,238
Commercial paper		10,154		—			10,154
Corporate bonds		5,069		(5	)		5,064
Certificates of deposit		1,960		—			1,960
Total available-for-sale investments	$	28,424	$	(8	)	$	28,416

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

15. Fair Value Measurements

The Company records certain financial assets and liabilities at fair value in accordance with the provisions of ASC Topic 820, Fair Value Measurements and Disclosures. As defined in the guidance, fair value, defined as an exit price, represents the amount that would be received to sell an asset or pay to transfer a liability in an orderly transaction between market participants. As a result, fair value is a market-based approach that should be determined based on assumptions that market participants would use in pricing an asset or a liability. As a basis for considering these assumptions, the guidance defines a three-tier value hierarchy that prioritizes the inputs used in the valuation methodologies in measuring fair value.

•

Level 1—Unadjusted quoted prices in active, accessible markets for identical assets or liabilities.

•

Level 2—Other inputs that are directly or indirectly observable in the marketplace.

•

Level 3—Unobservable inputs that are supported by little or no market activity.

The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value.

The Company’s material financial instruments at December 31, 2017 and 2016 consisted primarily of cash and cash equivalents, short-term investments and long-term debt and stock purchase warrant liabilities. The fair value of cash and cash equivalents, government bonds, other current assets and accounts payable approximate their respective carrying values due to the short term nature of these instruments and are classified as Level 1 in the fair hierarchy. The fair value of long-term debt approximates the carrying value due to variable interest rates that correspond to market rates. The Company has determined its short-term investments, comprised of certificates of deposit, corporate bonds, commercial paper, treasury bills and agency obligations, to be Level 2 in the fair value hierarchy. The fair value was determined using a market approach, based on prices and other relevant information generated by market transactions involving similar assets. The short-term investments consist of investments with original maturity dates from date of acquisition of 90 to 365 days and are classified as available-for-sale. The Company has determined its stock purchase warrants liability to be Level 3 in the fair value hierarchy.

There were no significant transfers between Levels 1, 2 and 3 during the years ended December 31, 2017 and 2016.

The following tables summarize the fair value of financial assets and liabilities that are measured at fair value and the classification by level of input within the fair value hierarchy (in thousands):

	December 31, 2017
	Level 1		Level 2		Level 3		Recorded Value
Financial Assets:
Cash and money markets	$	9,224	$	—	$	—	$	9,224
Restricted cash money market		360		—		—		360
Government bonds and treasury bills		11,238		—		—		11,238
Certificates of deposit		—		1,960		—		1,960
Corporate bonds		—		5,064		—		5,064
Commercial paper		—		10,154		—		10,154
Total financial assets	$	20,822	$	17,178	$	—	$	38,000

	December 31, 2016
	Level 1		Level 2		Level 3		Recorded Value
Financial Assets:
Cash and money markets	$	29,928	$	—	$	—	$	29,928
Restricted cash money market		360		—		—		360
Government bonds		19,027		—		—		19,027
Certificates of deposit		—		6,579		—		6,579
Agency obligations		—		4,179		—		4,179
Corporate bonds		—		7,262		—		7,262
Commercial paper		—		16,656		—		16,656
Total financial assets	$	49,315	$	34,676	$	—	$	83,991

Prior to the IPO, the Company estimated the fair value of its warrants to purchase preferred stock using an option pricing model that included three valuation scenarios, a non-IPO scenario and two IPO scenarios. Under the IPO scenarios, the Company calculated the value of the warrant based on a call option of the common share at IPO (assuming the underlying preferred stock would convert to common stock) given the time to exit and the term of the warrants stipulated in the contract. The Company then applied a discount for lack of marketability. Subsequent to the IPO, the Company used the Black-Scholes option pricing model to estimate the fair value of the remaining warrants. The estimates in the Black-Scholes option pricing model are based, in part, on assumptions related to the volatility of comparable public companies, the expected life of the warrants, the risk-free interest rate and the fair value of the underlying warrants. Changes in the fair value of the stock purchase warrants were recorded in other expense, net in the statements of operations. The following table summarizes the changes in fair value of the Level 3 liability, stock purchase warrants (in thousands):

	Level 3 Liabilities
	Year Ended December 31,
	2016
Stock purchase warrants
Balance at beginning of period	$	258
Issuance of stock purchase warrants		—
Exercise of stock purchase warrants		(414	)
Net increase in fair value remeasurement		156
Balance at end of period	$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Net Loss per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Loss Per Share

16. Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding for the period, without consideration of the dilutive effect of potential common stock equivalents. Diluted net loss per share gives effect to all dilutive potential shares of common stock outstanding during this period.

For all periods presented, the Company’s potential common stock equivalents, which included convertible preferred stock, stock options, unvested restricted stock and stock purchase warrants, have been excluded from the computation of diluted net loss per share as their inclusion would have the effect of reducing the net loss per share. Therefore, the denominator used to calculate both basic and diluted net loss per share is the same in all periods presented.

The Company’s potential common stock equivalents that have been excluded from the computation of diluted net loss per share for all periods presented because of their antidilutive effect consisted of the following:

	Year Ended December 31,
	2017		2016		2015
Convertible preferred stock		—		—		9,472,530
Outstanding stock options		3,075,349		2,243,575		1,261,637
Unvested restricted stock		—		—		6,485
Stock purchase warrants		29,796		29,796		146,298
		3,105,145		2,273,371		10,886,950

Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Data [Abstract]

Quarterly Financial Information (Unaudited)

17. Quarterly Financial Information (unaudited)

Summarized quarterly financial information for each of the years ended December 31, 2017 and 2016 are as follows (in thousands except per share data):

	Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Operating expenses	$	(10,261	)	$	(13,768	)	$	(18,348	)	$	(16,376	)
Net loss	$	(10,373	)	$	(13,773	)	$	(18,336	)	$	(16,493	)
Net loss per share of common stock — basic and diluted	$	(0.41	)	$	(0.54	)	$	(0.72	)	$	(0.65	)

	Quarter Ended
	March 31, 2016			June 30, 2016			September 30, 2016			December 31, 2016
Operating expenses	$	(5,862	)	$	(5,183	)	$	(5,311	)	$	(9,362	)
Net loss	$	(5,449	)	$	(5,102	)	$	(5,645	)	$	(9,686	)
Net loss per share of common stock — basic and diluted	$	(2.05	)	$	(0.62	)	$	(0.28	)	$	(0.45	)

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	18. Subsequent Events On March 12, 2018, the Company closed a follow-on public offering in which it sold 6,538,462 shares of common stock at a public offering price of $13.00 per share, resulting in net proceeds of $79.6 million after deducting underwriting discounts and commissions and estimated offering expenses. The Company has granted the underwriters of the offering an option, exercisable through April 6, 2018, to purchase up to an additional 980,769 shares of common stock at the public offering price.

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Presentation

The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

Use of Estimates

Segment Information

Property and Equipment, Net

Debt Discount

Fair Value Measurements

Income Taxes

Reverse Stock Split

Research and Development Costs

Research and development costs are charged to expense as incurred and include:

•

employee-related expenses, including salaries, benefits, travel and share-based compensation expense for research and development personnel;

•

expenses incurred under agreements with contract research organizations, contract manufacturing organizations and consultants that conduct clinical and preclinical studies;

•

costs associated with nonclinical and development activities;

•

costs associated with technology and intellectual property licenses;

•

costs for the Company’s research and development facility; and

•

depreciation expense for assets used in research and development activities.

Share-Based Compensation

Cash Equivalents

Cash equivalents consist of short-term, highly liquid investments with an original term of three months or less at the date of purchase.

Short-Term Investments

Restricted Cash

Concentration of Credit Risk Arising From Cash Deposits in Excess of Insured Limits

Recent Accounting Pronouncements

Accounting Pronouncements Recently Adopted

Recent Accounting Pronouncements Not Yet Adopted

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following (dollar amounts in thousands):

	Estimated Useful Lives (Years)	December31,
		2017			2016
Furniture and fixtures	5	$	303		$	69
Machinery and equipment	5		121			121
Computer equipment	3		41			27
Leasehold improvements	Lesser of useful life or remaining lease term		667			45
Total property and equipment			1,132			262
Less: Accumulated depreciation			(247	)		(168	)
Property and equipment, net		$	885		$	94

Accrued Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31,
	2017		2016
Accrued research and development	$	3,360	$	1,153
Accrued bonuses		920		870
Accrued professional fees		62		410
Accrued vacation		113		72
Accrued interest payable		58		52
Accrued expense		203		234
	$	4,716	$	2,791

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Scheduled Payments for the Loan Agreement

As of December 31, 2017, the scheduled payments for the loan agreement, including the scheduled final payment in 2020, were as follows (in thousands):

Year Ending December 31,	Principal		Interest and Final Payment		Total
2018	$	3,200	$	476	$	3,676
2019		3,200		234		3,434
2020		1,600		545		2,145
	$	8,000	$	1,255	$	9,255

Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2017

Temporary Equity Disclosure [Abstract]

Activity Convertible Preferred Stock

The following table summarizes the activity of convertible preferred stock (in thousands, except per share amounts):

																									Total
	Series A						Series A-1						Series B						Series C						Convertible
	Preferred Stock						Preferred Stock						Preferred Stock						Preferred Stock						Preferred
	Shares			Amount			Shares			Amount			Shares			Amount			Shares			Amount			Stock
Balance at January 1, 2016		5,198,826		$	4,086			4,356,931		$	7,900			6,009,202		$	15,372			5,274,674		$	19,956		$	47,314
Accretion of redeemable convertible preferred stock to redemption value		—			—			—			—			—			840			—			44			884
Conversion of preferred stock to common stock at closing of IPO		(5,198,826	)		(4,086	)		(4,356,931	)		(7,900	)		(6,009,202	)		(16,212	)		(5,274,674	)		(20,000	)		(48,198	)
Balance at December 31, 2016		—		$	—			—		$	—			—		$	—			—		$	—		$	—

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share-based Compensation Expense

The total share-based compensation expense recognized is reflected in the statements of operations as follows (in thousands):

	Year Ended December 31,
	2017		2016		2015

Research and development	$	1,348	$	539	$	327
General and administrative		1,988		775		378
Total	$	3,336	$	1,314	$	705

Weighted Average Assumptions Used in Fair Value Calculation for Underlying Common Stock

The following table sets forth the weighted average assumptions utilized in the fair value calculation for the underlying common stock for the years ended December 31, 2017, 2016 and 2015.

	Year Ended December 31,
	2017			2016			2015

Expected term (years)		7.00			7.00			7.00
Expected stock price volatility		96.85	%		97.45	%		86.63	%
Risk-free interest rate		2.20	%		2.20	%		2.09	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

Summary of Activity Related to Stock Options

The following table summarizes the activity related to stock options during the year ended December 31, 2017:

				Weighted
	Number of			Average
	Shares			Exercise Price

Options outstanding at January 1, 2017		2,243,575		$	5.78
Granted		1,127,950			6.45
Exercised		(171,926	)		1.37
Cancelled/Forfeited		(124,250	)		8.40
Options outstanding at December 31, 2017		3,075,349			6.17

Options exercisable at December 31, 2016		789,120			1.55

Options exercisable at December 31, 2017		1,114,286			3.94

Additional Information about the Stock Option Outstanding and Exercisable

The following table provides additional information about the Company’s stock options that were outstanding and exercisable at December 31, 2017 (aggregate intrinsic values in thousands):

							Weighted								Weighted
			Weighted				Average				Weighted				Average
			Average		Aggregate		Remaining				Average		Aggregate		Remaining
Exercise	Options		Exercise		Intrinsic		Contractual		Options		Exercise		Intrinsic		Contractual
Price	Outstanding		Price		Value		Life (Years)		Exercisable		Price		Value		Life (Years)

$0.02 - $0.40		465,265					5.4			465,265					5.4
$3.08 - $5.89		1,385,871					8.9			356,632					7.2
$6.16 - $8.90		1,105,921					8.9			264,161					8.2
$9.11 - $20.84		118,292						9.0		28,228					8.9
		3,075,349	$	6.17	$	5,598	8.4			1,114,286	$	3.94	$	4,180	6.7

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Net Deferred Tax Assets

Significant components of the Company’s net deferred income tax assets consist of the following (in thousands):

	December 31,
	2017			2016			2015
Deferred tax asset (liability)
Net operating loss carryforwards	$	27,999		$	23,391		$	14,119
Non-deductible accrued expenses		248			358			230
Deferred rent		49			1			4
Deferred revenue		38			69			77
Stock compensation expense		387			101			88
Depreciation differences		(18	)		(13	)		(28	)
Federal tax credits		3,437			1,232			850
State tax credits		524			301			262
Charitable contributions		6			6			3
Valuation allowance		(32,670	)		(25,446	)		(15,605	)
Net deferred tax asset	$	—		$	—		$	—

Schedule of Statutory and Effective Income Tax Rate Reconciliation

A reconciliation of the statutory tax rates and the effective tax rates is as follows:

	Year Ended December 31,
	2017			2016			2015
U.S. federal tax rate		34.00	%		34.00	%		34.00	%
State tax rate		2.42			3.79			4.54
Permanent difference and other		(2.84	)		(1.98	)		(1.26	)
Tax credit		3.97			1.62			2.66
Valuation allowance		(12.42	)		(37.43	)		(39.94	)
Impact of federal rate change		(25.13	)		—			—
		0.00	%		0.00	%		0.00	%

Commitment and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Future Minimum Commitments Due Under Non-Cancelable Operating Leases

Minimum lease payments were as follows at December 31, 2017 (in thousands):

Year ending December 31,
2018	$	431
2019		444
2020		458
2021		472
2022		487
Thereafter		373
Total minimum lease payments	$	2,665

Available-for-Sale Investments (Tables)

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Summary of Company's Available-For-Sale Investments

The following table summarizes the Company’s available-for-sale investments as of December 31, 2017 (in thousands):

	December 31, 2017
	Amortized		Unrealized			Fair
	Cost		Loss			Value

Government bonds and agency obligations	$	11,241	$	(3	)	$	11,238
Commercial paper		10,154		—			10,154
Corporate bonds		5,069		(5	)		5,064
Certificates of deposit		1,960		—			1,960
Total available-for-sale investments	$	28,424	$	(8	)	$	28,416

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value

	December 31, 2017
	Level 1		Level 2		Level 3		Recorded Value
Financial Assets:
Cash and money markets	$	9,224	$	—	$	—	$	9,224
Restricted cash money market		360		—		—		360
Government bonds and treasury bills		11,238		—		—		11,238
Certificates of deposit		—		1,960		—		1,960
Corporate bonds		—		5,064		—		5,064
Commercial paper		—		10,154		—		10,154
Total financial assets	$	20,822	$	17,178	$	—	$	38,000

	December 31, 2016
	Level 1		Level 2		Level 3		Recorded Value
Financial Assets:
Cash and money markets	$	29,928	$	—	$	—	$	29,928
Restricted cash money market		360		—		—		360
Government bonds		19,027		—		—		19,027
Certificates of deposit		—		6,579		—		6,579
Agency obligations		—		4,179		—		4,179
Corporate bonds		—		7,262		—		7,262
Commercial paper		—		16,656		—		16,656
Total financial assets	$	49,315	$	34,676	$	—	$	83,991

Summarizes the Changes in Fair Value of the Level 3 Liability, Stock Purchase Warrants

The following table summarizes the changes in fair value of the Level 3 liability, stock purchase warrants (in thousands):

	Level 3 Liabilities
	Year Ended December 31,
	2016
Stock purchase warrants
Balance at beginning of period	$	258
Issuance of stock purchase warrants		—
Exercise of stock purchase warrants		(414	)
Net increase in fair value remeasurement		156
Balance at end of period	$	—

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Potential Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share

	Year Ended December 31,
	2017		2016		2015
Convertible preferred stock		—		—		9,472,530
Outstanding stock options		3,075,349		2,243,575		1,261,637
Unvested restricted stock		—		—		6,485
Stock purchase warrants		29,796		29,796		146,298
		3,105,145		2,273,371		10,886,950

Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Data [Abstract]

Summary of Quarterly Financial Information

Summarized quarterly financial information for each of the years ended December 31, 2017 and 2016 are as follows (in thousands except per share data):

	Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Operating expenses	$	(10,261	)	$	(13,768	)	$	(18,348	)	$	(16,376	)
Net loss	$	(10,373	)	$	(13,773	)	$	(18,336	)	$	(16,493	)
Net loss per share of common stock — basic and diluted	$	(0.41	)	$	(0.54	)	$	(0.72	)	$	(0.65	)

	Quarter Ended
	March 31, 2016			June 30, 2016			September 30, 2016			December 31, 2016
Operating expenses	$	(5,862	)	$	(5,183	)	$	(5,311	)	$	(9,362	)
Net loss	$	(5,449	)	$	(5,102	)	$	(5,645	)	$	(9,686	)
Net loss per share of common stock — basic and diluted	$	(2.05	)	$	(0.62	)	$	(0.28	)	$	(0.45	)

The Company - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands						12 Months Ended
	Mar. 12, 2018	Jun. 30, 2017	Jan. 06, 2017	Dec. 14, 2016	Jun. 07, 2016	Dec. 31, 2017	Dec. 31, 2016	Jul. 06, 2016
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Entity incorporation date						May 26, 2011
Common stock, Sale of shares						25,354,651	24,573,033
Common stock, Share offering price				$ 9.00
Underwriting discounts and commissions				$ 2,500
Offering expense			$ 400
Public offering closing date				Dec. 14, 2016
Issuance of common stock for follow-on public offering, shares				4,000,000
Issuance of common stock for follow-on public offering, value				$ 33,400		$ 5,057	$ 33,459
Issuance of common stock in initial public offering							$ 51,377
Proceeds from Issuance of convertible preferred stock and long-term debt						53,900
Cash, cash equivalents and short-term investments						$ 37,600
Subsequent Event
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Common stock, Share offering price	$ 13.00
Public offering closing date	Mar. 12, 2018
Issuance of common stock for follow-on public offering, shares	6,538,462
Net proceeds after deducting underwriting discounts and commissions and estimated offering expenses	$ 79,600
Common Stock
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Common stock, Sale of shares							8,148,843
Issuance of common stock for follow-on public offering, shares						600,000	4,000,000
Issuance of common stock for follow-on public offering, value							$ 4
Issuance of common stock in initial public offering							$ 8
IPO
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
IPO, closing date						Jun. 07, 2016
Common stock, Sale of shares					7,200,000
Common stock, Share offering price					$ 7.00
Net proceeds from issuance of stock					$ 45,300
Underwriting discounts and commissions						$ 4,000
Offering expense						1,600
Net offering proceeds after deducting underwriting discount and commission and offering expenses						$ 51,400
Over-allotment option by underwriters
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Common stock, Sale of shares			600,000					948,843
Common stock, Share offering price			$ 9.00					$ 7.00
Net proceeds from issuance of stock			$ 5,100					$ 6,100
Over-allotment option by underwriters \| Subsequent Event
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Common stock, Share offering price	$ 13.00
Issuance of common stock for follow-on public offering, shares	6,538,462
Net proceeds after deducting underwriting discounts and commissions and estimated offering expenses	$ 79,600
At-the-market sales agreement \| Cowen and Company LLC \| Common Stock
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of shares sold under facility		0
At-the-market sales agreement \| Cowen and Company LLC \| Common Stock \| Maximum
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Issuance of common stock in initial public offering		$ 50,000

Significant Accounting Policies - Additional Information (Detail) $ in Millions		12 Months Ended
	May 11, 2016	Dec. 31, 2017 USD ($) Segment
Accounting Policies [Abstract]
Number of operating segments \| Segment		1
Cumulative net operating losses \| $		$ 28.0
Reverse split of common stock	0.4545
Reverse stock split ratio		On May 11, 2016, the Company effected a 1-for-2.2 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s convertible preferred stock.
Short-term investments maturity start period		90 days
Short-term investments maturity end period		365 days

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and Equipment, gross	$ 1,132	$ 262
Less: Accumulated depreciation	(247)	(168)
Property and equipment, net	885	94
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and Equipment, gross	$ 303	69
Estimated Useful Lives (Years)	5 years
Machinery and Equipment
Property Plant And Equipment [Line Items]
Property and Equipment, gross	$ 121	121
Estimated Useful Lives (Years)	5 years
Computer Equipment
Property Plant And Equipment [Line Items]
Property and Equipment, gross	$ 41	27
Estimated Useful Lives (Years)	3 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and Equipment, gross	$ 667	$ 45
Estimated Useful Lives (Years)	Lesser of useful life or remaining lease term

Accrued Liabilities - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued research and development	$ 3,360	$ 1,153
Accrued bonuses	920	870
Accrued professional fees	62	410
Accrued vacation	113	72
Accrued interest payable	58	52
Accrued expense	203	234
Accrued liabilities, current	$ 4,716	$ 2,791

Long-Term Debt - Additional Information (Details) - USD ($)		1 Months Ended		12 Months Ended
	Sep. 28, 2016	Sep. 30, 2016	Apr. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 15, 2015	Apr. 15, 2015	Apr. 01, 2015
Debt Instrument [Line Items]
Long term debt				$ 8,000,000
Interest expense on borrowings				653,000	$ 287,000	$ 115,000
Accretion of scheduled final payment				211,000	283,000	101,000
Accretion of deferred closing costs				$ 62,000	$ 17,000	$ 7,400
Silicon Valley Bank
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity									$ 6,000,000
Long term debt							$ 2,000,000	$ 4,000,000
Long term debt, maturity year			2018
Debt Instrument, Payment Terms				The Company was required to pay accrued interest only for a period of 12 months from the date of each advance, followed by 30 equal monthly payments of principal and accrued interest.
Final payment during maturity			$ 300,000
Final payment during maturity, percentage			5.50%
Closing costs recorded in the long-term debt liability			$ 24,000
Silicon Valley Bank , MidCap Funding XII Trust and MidCap Financial Trust
Debt Instrument [Line Items]
Long term debt	$ 8,000,000
Debt Instrument, Payment Terms				The Company was required to pay accrued interest only through December 31, 2017 on the outstanding amount, followed by 30 equal payments of principal and accrued interest.
Final payment during maturity				$ 500,000
Final payment during maturity, percentage				6.50%
Line of credit facility, remaining borrowing capacity				$ 7,000,000
Debt instrument, maturity date				Jun. 01, 2020
Repay all the amount outstanding under the original loan agreement	$ 5,300,000
Silicon Valley Bank , MidCap Funding XII Trust and MidCap Financial Trust \| Prepayments Through May 31, 2020
Debt Instrument [Line Items]
Prepayment fee percentage of the original principal amount of the aggregate term loans		2.00%
Silicon Valley Bank , MidCap Funding XII Trust and MidCap Financial Trust \| Amended and Restated Loan and Security Agreement
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 15,000,000
Interest rate		0.50%
Debt instrument, description of variable rate basis				30-day U.S. LIBOR
Prime Rate \| Silicon Valley Bank
Debt Instrument [Line Items]
Interest rate			0.50%
Floating Interest Rate \| Silicon Valley Bank , MidCap Funding XII Trust and MidCap Financial Trust \| Amended and Restated Loan and Security Agreement
Debt Instrument [Line Items]
Interest rate		7.00%

Long-Term Debt - Scheduled Payments for Loan Agreement (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Debt Disclosure [Abstract]
Principal, 2018	$ 3,200
Principal, 2019	3,200
Principal, 2020	1,600
Principal	8,000
Interest and Final Payment, 2018	476
Interest and Final Payment, 2019	234
Interest and Final Payment, 2020	545
Interest and Final Payment	1,255
Total, 2018	3,676
Total, 2019	3,434
Total, 2020	2,145
Total	$ 9,255

Convertible Shareholder Notes Payable (Detail) - The Bridge Notes	1 Months Ended
	Aug. 31, 2014 $ / shares shares	Apr. 30, 2014 USD ($) Stockholder
Class Of Stock [Line Items]
Convertible notes principal amount authorized \| $		$ 6,000,000
Issuance of promissory notes \| $		$ 3,000,000
Debt instrument annual interest rate		7.00%
Debt instrument, maturity date		Apr. 30, 2015
Warrants issued to purchase common stock shares	112,802
Class of warrant Exercise \| $ / shares	$ 0.02
Series B Preferred Stock
Class Of Stock [Line Items]
Debt converted into shares of convertible preferred stock	1,137,652
Convertible Stock Warrant
Class Of Stock [Line Items]
Number of shares, exercised	112,441
Executive Officer
Class Of Stock [Line Items]
Number of stockholders \| Stockholder		2
Director
Class Of Stock [Line Items]
Number of stockholders \| Stockholder		1

Convertible Preferred Stock - Additional Information (Detail) - $ / shares	Dec. 31, 2017	Dec. 31, 2016	Jun. 07, 2016	Dec. 31, 2015
Class Of Stock [Line Items]
Preferred stock convertible into common stock			9,614,159
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series A, A-1, B and C Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized				20,913,331
Convertible preferred stock, par value				$ 0.001
Convertible Preferred Stock \| IPO
Class Of Stock [Line Items]
Convertible preferred stock, shares issued			20,839,633
Convertible preferred stock, shares outstanding			20,839,633

Convertible Preferred Stock (Detail) $ in Thousands	12 Months Ended
Convertible Preferred Stock (Detail) $ in Thousands	Dec. 31, 2016 USD ($) shares
Class Of Stock [Line Items]
Beginning balance	$ 47,314
Accretion of redeemable convertible preferred stock to redemption value	884
Conversion of preferred stock to common stock at closing of IPO	(48,198)
Series A
Class Of Stock [Line Items]
Beginning balance	$ 4,086
Beginning balance, shares \| shares	5,198,826
Conversion of preferred stock to common stock at closing of IPO	$ (4,086)
Conversion of preferred stock to common stock at closing of IPO, shares \| shares	(5,198,826)
Series A-1 Preferred Stock
Class Of Stock [Line Items]
Beginning balance	$ 7,900
Beginning balance, shares \| shares	4,356,931
Conversion of preferred stock to common stock at closing of IPO	$ (7,900)
Conversion of preferred stock to common stock at closing of IPO, shares \| shares	(4,356,931)
Series B
Class Of Stock [Line Items]
Beginning balance	$ 15,372
Beginning balance, shares \| shares	6,009,202
Accretion of redeemable convertible preferred stock to redemption value	$ 840
Conversion of preferred stock to common stock at closing of IPO	$ (16,212)
Conversion of preferred stock to common stock at closing of IPO, shares \| shares	(6,009,202)
Series C
Class Of Stock [Line Items]
Beginning balance	$ 19,956
Beginning balance, shares \| shares	5,274,674
Accretion of redeemable convertible preferred stock to redemption value	$ 44
Conversion of preferred stock to common stock at closing of IPO	$ (20,000)
Conversion of preferred stock to common stock at closing of IPO, shares \| shares	(5,274,674)

Common Stock - Additional Information (Detail) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Common stock, shares authorized	100,000,000	100,000,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares outstanding	25,354,651	24,573,033

Stock Purchase Warrants - Additional Information (Details) - USD ($)			1 Months Ended		12 Months Ended
	Oct. 12, 2016	Jun. 06, 2016	Sep. 30, 2016	Apr. 30, 2015	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Preferred Stock Warrants \| Series A-1 Preferred Stock
Class Of Warrant Or Right [Line Items]
Class of warrant Exercise								$ 1.8132
Warrant exercisable term								10 years
Weighted average remaining life of warrants						6 years 9 months 18 days
Fair value of warrant						$ 58,000
Number of shares, exercised		3,236
Preferred Stock Warrants \| Series B Preferred Stock
Class Of Warrant Or Right [Line Items]
Class of warrant Exercise				$ 3.50
Warrant exercisable term				10 years
Weighted average remaining life of warrants						9 years 3 months
Fair value of warrant						$ 200,000
Number of shares, exercised	17,883
Preferred Stock Warrants \| Series B Preferred Stock \| Convertible Warrant
Class Of Warrant Or Right [Line Items]
Number of stock that can be purchased by each warrant				25,974
Class of warrant Exercise				$ 7.70
Preferred Stock Warrants \| Maximum \| Series A-1 Preferred Stock
Class Of Warrant Or Right [Line Items]
Number of stock that can be purchased by each warrant								16,550
Preferred Stock Warrants \| Maximum \| Series B Preferred Stock
Class Of Warrant Or Right [Line Items]
Number of stock that can be purchased by each warrant				57,143
Convertible Stock Warrant \| Convertible Promissory Note
Class Of Warrant Or Right [Line Items]
Class of warrant Exercise							$ 0.02
Weighted average remaining life of warrants							8 years 2 months 12 days
Number of shares, exercised		112,441
Convertible Stock Warrant \| Amended and Restated Loan And Security Agreement
Class Of Warrant Or Right [Line Items]
Class of warrant Exercise			$ 10.74
Weighted average remaining life of warrants					8 years 9 months
Warrants expiration term			2026-09
Convertible Stock Warrant \| Maximum \| Convertible Promissory Note
Class Of Warrant Or Right [Line Items]
Number of stock that can be purchased by each warrant							112,802
Convertible Stock Warrant \| Maximum \| Amended and Restated Loan And Security Agreement
Class Of Warrant Or Right [Line Items]
Number of stock that can be purchased by each warrant			29,796

Share-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jan. 01, 2018	Jan. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 29, 2017
2016 Stock Incentive Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares common stock reserved for issuance	1,765,264
Annual increase of common stock reserved for issuance	4.00%
Increase in common stock for future issuance, shares	1,014,186
2016 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares common stock reserved for issuance		181,818
Share based compensation arrangement description			the number of shares reserved for issuance under the 2016 ESPP will automatically increase for a period of ten years, from January 1, 2017 through January 1, 2026, by the lesser of (i) 1% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, (ii) 454,545 shares of common stock or (iii) a lesser number of shares as may be determined by the Company’s board of directors.
Annual increase of common stock reserved for issuance		1.00%
Employee payroll deductions, percent		15.00%
Number of shares reserved for issuance increase in years		10 years
Addition of common stock shares reserved for future issuance		454,545
Common stock purchased			9,692
2016 Employee Stock Purchase Plan \| General and Administrative Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense			$ 21,000
2016 Employee Stock Purchase Plan \| Research and Development Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense			$ 7,000
2016 Employee Stock Purchase Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares common stock reserved for issuance	671,402
Annual increase of common stock reserved for issuance	1.00%
Addition of common stock shares reserved for future issuance	253,546
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares grants			1,127,950
Option to purchase common stock shares outstanding			3,075,349	2,243,575
Weighted average exercise price			$ 6.17	$ 5.78
Unrecognized compensation expense related to unvested stock options			$ 11,600
Expected to be recognized over a weighted average period			3 years 1 month 6 days
Weighted-average fair values granted			$ 5.25	$ 7.89	$ 5.72
Fair market value per share of common stock						$ 7.00
Share-based compensation expense			$ 3,336	$ 1,314	$ 705
Stock Options \| General and Administrative Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense			1,988	775	378
Stock Options \| Research and Development Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense			$ 1,348	$ 539	$ 327
Stock Options \| 2016 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares common stock reserved for issuance		1,818,182
Share based compensation arrangement description			The number of shares of common stock reserved for issuance under the 2016 Plan will automatically increase on January 1 each year, for a period of ten years, from January 1, 2017 through January 1, 2026, by 4% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors.
Annual increase of common stock reserved for issuance			4.00%
Option to purchase common stock shares outstanding			2,044,400
Weighted average exercise price			$ 7.98
Shares available for future grant			751,078
Stock Options \| 2011 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares grants			0
Option to purchase common stock shares outstanding			1,013,713
Weighted average exercise price			$ 2.47

Share-Based Compensation - Summary of Share-based Compensation Expense (Details) - Stock Options - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 3,336	$ 1,314	$ 705
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	1,348	539	327
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 1,988	$ 775	$ 378

Share-Based Compensation - Weighted Average Assumptions Used in Fair Value Calculation for Underlying Common Stock (Details) - Stock Options	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (years)	7 years	7 years	7 years
Expected stock price volatility	96.85%	97.45%	86.63%
Risk-free interest rate	2.20%	2.20%	2.09%
Expected dividend yield	0.00%	0.00%	0.00%

Share-Based Compensation - Summary of Activity Related to Stock Options (Details) - Stock Options - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Options outstanding, Beginning balance	2,243,575
Number of Shares, Granted	1,127,950
Number of Shares, Exercised	(171,926)
Number of Shares, Cancelled/Forfeited	(124,250)
Number of Shares, Options outstanding, Ending balance	3,075,349	2,243,575
Number of Shares, Options exercisable	1,114,286	789,120
Weighted Average Exercise Price, Options outstanding, Beginning balance	$ 5.78
Weighted Average Exercise Price, Granted	6.45
Weighted Average Exercise Price, Exercised	1.37
Weighted Average Exercise Price, Cancelled/Forfeited	8.40
Weighted Average Exercise Price, Options outstanding, Ending balance	6.17	$ 5.78
Weighted Average Exercise Price, Options exercisable	$ 3.94	$ 1.55

Share-Based Compensation - Additional Information about the Stock Option Outstanding and Exercisable (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding	3,075,349	2,243,575
Weighted Average Exercise Price	$ 6.17	$ 5.78
Aggregate Intrinsic Value	$ 5,598
Weighted Average Remaining Contractual Life (Years)	8 years 4 months 24 days
Options Exercisable	1,114,286	789,120
Weighted Average Exercise Price	$ 3.94	$ 1.55
Aggregate Intrinsic Value	$ 4,180
Weighted Average Remaining Contractual Life (Years)	6 years 8 months 12 days
$0.02 - $0.40
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 0.02
Exercise Price Upper Range Limit	$ 0.40
Options Outstanding	465,265
Weighted Average Remaining Contractual Life (Years)	5 years 4 months 24 days
Options Exercisable	465,265
Weighted Average Remaining Contractual Life (Years)	5 years 4 months 24 days
$3.08 - $5.89
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 3.08
Exercise Price Upper Range Limit	$ 5.89
Options Outstanding	1,385,871
Weighted Average Remaining Contractual Life (Years)	8 years 10 months 24 days
Options Exercisable	356,632
Weighted Average Remaining Contractual Life (Years)	7 years 2 months 12 days
$6.16 - $8.90
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 6.16
Exercise Price Upper Range Limit	$ 8.90
Options Outstanding	1,105,921
Weighted Average Remaining Contractual Life (Years)	8 years 10 months 24 days
Options Exercisable	264,161
Weighted Average Remaining Contractual Life (Years)	8 years 2 months 12 days
$9.11 - $20.84
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range Limit	$ 9.11
Exercise Price Upper Range Limit	$ 20.84
Options Outstanding	118,292
Weighted Average Remaining Contractual Life (Years)	9 years
Options Exercisable	28,228
Weighted Average Remaining Contractual Life (Years)	8 years 10 months 24 days

Income Tax - Additional Information (Detail) - USD ($)	12 Months Ended
Income Tax - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
U.S. federal tax rate		34.00%	34.00%	34.00%
Tax Cuts and Jobs Act of 2017,Provisional Income Tax Expense		$ 14,900,000
Increase in deferred income tax valuation allowance		7,200,000	$ 9,800,000	$ 7,000,000
Net deferred tax assets related to net operating loss carryforwards		$ 27,999,000	$ 23,391,000	$ 14,119,000
Net deferred tax assets related to net operating loss carryforwards expiration year		2037
Scenario, Plan
Income Tax Disclosure [Line Items]
U.S. federal tax rate	21.00%
U.S. Federal or State Income Taxes [Member]
Income Tax Disclosure [Line Items]
Provision for income taxes		$ 0

Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax asset (liability)
Net operating loss carryforwards	$ 27,999	$ 23,391	$ 14,119
Deferred tax asset (liability) Non-deductible accrued expenses	248	358	230
Deferred rent	49	1	4
Deferred revenue	38	69	77
Stock compensation expense	387	101	88
Depreciation differences	(18)	(13)	(28)
Charitable contributions	6	6	3
Valuation allowance	(32,670)	(25,446)	(15,605)
Federal
Deferred tax asset (liability)
Tax credits	3,437	1,232	850
State
Deferred tax asset (liability)
Tax credits	$ 524	$ 301	$ 262

Schedule of Statutory and Effective Income Tax Rate Reconciliation (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. federal tax rate	34.00%	34.00%	34.00%
State tax rate	2.42%	3.79%	4.54%
Permanent difference and other	(2.84%)	(1.98%)	(1.26%)
Tax credit	3.97%	1.62%	2.66%
Valuation allowance	(12.42%)	(37.43%)	(39.94%)
Impact of federal rate change	(25.13%)
Total income tax provision (benefit)	0.00%	0.00%	0.00%

Commitment and Contingencies - Additional Information (Details)	1 Months Ended	12 Months Ended
	Nov. 30, 2016 USD ($) ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitment And Contingencies [Line Items]
Non-cancelable operating leases, expiration date		2017-03
Rent expense		$ 214,000	$ 81,000	$ 150,000
GEORGIA
Commitment And Contingencies [Line Items]
Area of office leased \| ft²	20,000
Operating lease agreement term	6 years 6 months
Operating lease agreement renewal option term	5 years
Minimum monthly lease payments	$ 35,145
Percentage of increase per year	3.00%

Commitment and Contingencies - Future Minimum Commitments Due Under Non-Cancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 431
2019	444
2020	458
2021	472
2022	487
Thereafter	373
Total minimum lease payments	$ 2,665

License and Collaboration Agreements - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Apr. 30, 2015	Aug. 31, 2014
Research And Development Arrangement Contract To Perform For Others [Line Items]
Revenue from collaborative agreements		$ 325,000
NovaMedica
Research And Development Arrangement Contract To Perform For Others [Line Items]
License revenue		$ 20,000	$ 20,000
Patent expirations period		2027
NovaMedica \| Upfront payment
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue	$ 200,000				$ 200,000
Spark Therapeutics, Inc. \| Upfront payment
Research And Development Arrangement Contract To Perform For Others [Line Items]
License revenue	$ 500,000
Upfront, non-refundable payment				$ 500,000
Rusnano MedInvest LLC
Research And Development Arrangement Contract To Perform For Others [Line Items]
Percentage of voting securities owned subsidiary		6.00%

Available-for-Sale Investments - Summary of Company's Available-For-Sale Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 28,424
Unrealized Loss	(8)
Fair Value	28,416	$ 48,807
Government Bonds and Agency Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,241
Unrealized Loss	(3)
Fair Value	11,238
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,154
Fair Value	10,154
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,960
Fair Value	1,960
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,069
Unrealized Loss	(5)
Fair Value	$ 5,064

Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Short-term investments maturity start period	90 days
Short-term investments maturity end period	365 days
Significant transfers between Levels 1, 2 and 3	$ 0	$ 0

Fair Value Measurements - Summary of Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial Assets:
Total financial assets	$ 38,000	$ 83,991
Government Bonds and Treasury Bills
Financial Assets:
Total financial assets	11,238
Corporate Bonds
Financial Assets:
Total financial assets	5,064	7,262
Commercial Paper
Financial Assets:
Total financial assets	10,154	16,656
Level 1
Financial Assets:
Total financial assets	20,822	49,315
Level 1 \| Government Bonds and Treasury Bills
Financial Assets:
Total financial assets	11,238
Level 2
Financial Assets:
Total financial assets	17,178	34,676
Level 2 \| Corporate Bonds
Financial Assets:
Total financial assets	5,064	7,262
Level 2 \| Commercial Paper
Financial Assets:
Total financial assets	10,154	16,656
Cash and Money Markets
Financial Assets:
Total financial assets	9,224	29,928
Cash and Money Markets \| Level 1
Financial Assets:
Total financial assets	9,224	29,928
Restricted Cash Money Market
Financial Assets:
Total financial assets	360	360
Restricted Cash Money Market \| Level 1
Financial Assets:
Total financial assets	360	360
Certificates of Deposit
Financial Assets:
Total financial assets	1,960	6,579
Certificates of Deposit \| Level 2
Financial Assets:
Total financial assets	$ 1,960	6,579
Government Bonds
Financial Assets:
Total financial assets		19,027
Government Bonds \| Level 1
Financial Assets:
Total financial assets		19,027
Agency Obligations
Financial Assets:
Total financial assets		4,179
Agency Obligations \| Level 2
Financial Assets:
Total financial assets		$ 4,179

Fair Value Measurements - Summarizes the Changes in Fair Value of the Level 3 Liability, Stock Purchase Warrants (Detail) - Stock Purchase Warrants $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Stock purchase warrants
Balance at beginning of period	$ 258
Exercise of stock purchase warrants	(414)
Net increase in fair value remeasurement	$ 156

Net Loss Per Share - Potential Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,105,145	2,273,371	10,886,950
Outstanding Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,075,349	2,243,575	1,261,637
Unvested Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share			6,485
Stock Purchase Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	29,796	29,796	146,298
Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share			9,472,530

Quarterly Financial Information (Unaudited) - Summary of Quarterly Financial Information - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Operating expenses	$ (16,376)	$ (18,348)	$ (13,768)	$ (10,261)	$ (9,362)	$ (5,311)	$ (5,183)	$ (5,862)	$ (58,753)	$ (25,718)	$ (17,317)
Net loss	$ (16,493)	$ (18,336)	$ (13,773)	$ (10,373)	$ (9,686)	$ (5,645)	$ (5,102)	$ (5,449)	$ (58,975)	$ (25,882)	$ (17,639)
Net loss per share of common stock — basic and diluted	$ (0.65)	$ (0.72)	$ (0.54)	$ (0.41)	$ (0.45)	$ (0.28)	$ (0.62)	$ (2.05)	$ (2.33)	$ (1.97)	$ (7.54)

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Mar. 12, 2018	Dec. 14, 2016	Jan. 06, 2017	Jul. 06, 2016
Subsequent Event [Line Items]
Issuance of common stock for follow-on public offering, shares		4,000,000
Common stock, Share offering price		$ 9.00
Over-allotment option by underwriters
Subsequent Event [Line Items]
Common stock, Share offering price			$ 9.00	$ 7.00
Subsequent Event
Subsequent Event [Line Items]
Issuance of common stock for follow-on public offering, shares	6,538,462
Common stock, Share offering price	$ 13.00
Net proceeds after deducting underwriting discounts and commissions and estimated offering expenses	$ 79.6
Subsequent Event \| Over-allotment option by underwriters
Subsequent Event [Line Items]
Issuance of common stock for follow-on public offering, shares	6,538,462
Common stock, Share offering price	$ 13.00
Net proceeds after deducting underwriting discounts and commissions and estimated offering expenses	$ 79.6
Common stock exercisable date	Apr. 06, 2018
Subsequent Event \| Over-allotment option by underwriters \| Maximum
Subsequent Event [Line Items]
Additional shares of common stock issuable to underwriters	980,769