Protagonist Therapeutics (PTGX) 10-K 7 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 28, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	PTGX
Entity Registrant Name	PROTAGONIST THERAPEUTICS, INC.
Entity Central Index Key	1,377,121
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	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		16,787,990
Entity Public Float			$ 0

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 21,084	$ 4,055
Restricted cash	10	10
Available-for-sale securities - current	56,515	7,868
Research and development tax incentive receivable	2,241	715
Prepaid expenses and other current assets	3,394	1,558
Total current assets	83,244
Property and equipment, net	562	609
Available-for-sale securities - noncurrent	10,150
Other assets	34	30
Total assets	93,990	14,845
Current liabilities:
Accounts payable	1,163	1,247
Accrued expenses and other payables	5,272	1,879
Total current liabilities	6,435	3,126
Redeemable convertible preferred stock tranche liability		1,643
Redeemable convertible preferred stock warrant liability		480
Total liabilities	6,435	5,249
Commitments and contingencies
Redeemable convertible preferred stock		36,996
Stockholders' equity (deficit):
Preferred stock, $0.00001 par value, 10,000,000 and no shares authorized as of December 31, 2016 and 2015, respectively; and no shares issued and outstanding as of December 31, 2016 and 2015
Common stock, $0.00001 par value, 90,000,000 and 160,000,000 shares authorized as of December 31, 2016 and, 2015, respectively; 16,722,280 and 272,409 shares issued and outstanding as of December 31, 2016 and 2015, respectively	0	0
Additional paid-in capital	152,393	118
Accumulated other comprehensive loss	(245)	(102)
Accumulated deficit	(64,593)	(27,416)
Total stockholders' equity (deficit)	87,555	(27,400)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 93,990	$ 14,845

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Redeemable convertible preferred stock, par value	$ 0.00001	$ 0.00001
Redeemable convertible preferred stock, shares authorized	0	126,374,911
Redeemable convertible preferred stock, shares issued	0	77,185,117
Redeemable convertible preferred stock, shares outstanding	0	77,185,117
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	90,000,000	160,000,000
Common stock, shares issued	16,722,280	272,409
Common stock, shares outstanding	16,722,280	272,409

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 25,705	$ 11,831	$ 7,459
General and administrative	6,961	2,963	1,860
Total operating expenses	32,666	14,794	9,319
Loss from operations	(32,666)	(14,794)	(9,319)
Interest income	242	19	16
Change in fair value of redeemable convertible preferred stock tranche and warrant liabilities	(4,719)	(83)	(1,769)
Other expense	(34)
Net loss	(37,177)	(14,858)	(11,072)
Net loss attributable to common stockholders	$ (37,735)	$ (14,933)	$ (11,218)
Net loss per share attributable to common stockholders, basic and diluted	$ (5.80)	$ (59.32)	$ (49.38)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	6,501,796	251,717	227,197

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (37,177)	$ (14,858)	$ (11,072)
Other comprehensive loss:
(Loss) gain on translation of foreign operations	(76)	3	(54)
Unrecognized loss on available-for-sale securities	(67)	(5)
Comprehensive loss	$ (37,320)	$ (14,860)	$ (11,126)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock [Member]	Series B Preferred Stock [Member]	Series C Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2013		$ 9,122
Balance, Shares at Dec. 31, 2013		24,037,500
Issuance of Series B redeemable convertible preferred stock			$ 9,000
Issuance of Series B redeemable convertible preferred stock, Shares			18,000,000
Settlement of fair value of redeemable convertible preferred stock tranche liability			$ 2,308
Accretion of redemption of convertible preferred stock to redemption value	$ 146	$ 146
Balance at Dec. 31, 2014		$ 20,576
Balance, Shares at Dec. 31, 2014		42,037,500
Balance at Dec. 31, 2013	(1,394)					$ 135	$ (46)	$ (1,483)
Balance, Shares at Dec. 31, 2013					226,009
Accretion of redeemable convertible preferred stock to redemption value	(146)					(143)		(3)
Stock-based compensation expense	42					42
Issuance of common stock upon the exercise of options	3					3
Issuance of common stock upon the exercise of options, Shares					2,548
Other comprehensive loss	(54)						(54)
Net loss	(11,072)							(11,072)
Balance at Dec. 31, 2014	(12,621)					37	(100)	(12,558)
Balance, Shares at Dec. 31, 2014					228,557
Issuance of Series B redeemable convertible preferred stock				$ 16,345
Issuance of Series B redeemable convertible preferred stock, Shares				35,147,617
Accretion of redemption of convertible preferred stock to redemption value	75	$ 75
Balance at Dec. 31, 2015	$ 36,996	$ 36,996
Balance, Shares at Dec. 31, 2015	77,185,117	77,185,117
Accretion of redeemable convertible preferred stock to redemption value	$ (75)					(75)
Stock-based compensation expense	99					99
Issuance of common stock upon the exercise of options	57					57
Issuance of common stock upon the exercise of options, Shares					43,852
Other comprehensive loss	(2)						(2)
Net loss	(14,858)							(14,858)
Balance at Dec. 31, 2015	$ (27,400)					118	(102)	(27,416)
Balance, Shares at Dec. 31, 2015	272,409				272,409
Exercise of redeemable convertible preferred stock warrant liability		$ 1,025
Exercise of redeemable convertible preferred stock warrant liability, Shares		1,999,998
Issuance of Series B redeemable convertible preferred stock				$ 22,488
Issuance of Series B redeemable convertible preferred stock, Shares				45,189,794
Settlement of fair value of redeemable convertible preferred stock tranche liability	$ 5,837
Accretion of redemption of convertible preferred stock to redemption value	$ 558	$ 558
Balance, Shares at Dec. 31, 2016	0
Accretion of redeemable convertible preferred stock to redemption value	$ (558)					(558)
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering	66,904	$ (66,904)				66,904
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering, Shares		(124,374,909)			8,577,571
Issuance of common stock upon initial public offering, net of issuance costs	83,648					83,648
Issuance of common stock upon initial public offering, net of issuance costs, Shares					7,752,972
Stock-based compensation expense	2,130					2,130
Issuance of common stock upon the exercise of options	151					151
Issuance of common stock upon the exercise of options, Shares					119,328
Other comprehensive loss	(143)						(143)
Net loss	(37,177)							(37,177)
Balance at Dec. 31, 2016	$ 87,555					$ 152,393	$ (245)	$ (64,593)
Balance, Shares at Dec. 31, 2016	16,722,280				16,722,280

Consolidated Statements of Red7

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Reclassification to redeemable convertible preferred stock tranche liability	$ 1,017
Series C Preferred Stock [Member]
Issuance of convertible redeemable preferred stock, net issuance costs	138
Reclassification to redeemable convertible preferred stock tranche liability	$ 1,017

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTITIVIES
Net loss	$ (37,177)	$ (14,858)	$ (11,072)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	317	247	258
Loss on disposal of property and equipment	34
Amortization of premium on available-for-sale securities	117	(8)
Stock-based compensation	2,130	99	42
Change in fair value associated with redeemable convertible preferred stock tranche liability	4,194	626	897
Change in fair value of redeemable convertible preferred stock warrant liability	525	(543)	872
Changes in operating assets and liabilities:
Research and development tax credit receivable	(1,588)	(192)	259
Prepaid expenses and other current assets	(1,800)	(1,502)	604
Other assets	(4)	(30)
Accounts payable	(115)	898	179
Accrued expenses and other payables	3,395	878	218
Net cash used in operating activities	(29,972)	(14,385)	(7,743)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of available-for-sale securities	(73,169)	(7,865)
Purchase of property and equipment	(379)	(399)	(299)
Proceeds from maturities of available-for-sale securities	14,188
Proceeds from sale of property and equipment	32
Net cash used in investing activities	(59,328)	(8,264)	(299)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	22,488	17,362	9,000
Proceeds from issuance of redeemable convertible preferred stock upon exercise of preferred stock warrant liability	20
Proceeds from issuance of common stock upon exercise of stock options	151	57	3
Proceeds from issuance of common stock upon initial public offering, net of issuance costs	83,648
Net cash provided by financing activities	106,307	17,419	9,003
Effect on exchange rate changes on cash and cash equivalents	22	(39)	(97)
Net increase (decrease) in cash and cash equivalents	17,029	(5,269)	864
Cash and cash equivalents, beginning of year	4,055	9,324	8,460
Cash and cash equivalents, end of year	21,084	4,055	9,324
SUPPLEMENTAL DISCLOSURES OF NON-CASH FINANCING INFORMATION:
Settlement of fair value of redeemable convertible preferred stock liability	5,837		2,308
Tranche liability in connection with the Series C redeemable convertible preferred stock financing		1,017
Accretion of redeemable convertible preferred stock	558	$ 75	$ 146
Conversion of redeemable convertible preferred stock to common stock at closing of initial public offering	66,904
Reclassification of preferred stock warrant liability to equity	1,005
Purchase of property and equipment in accounts payable	$ 21

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business Protagonist Therapeutics, Inc. (the “Company”) was incorporated in the state of Delaware on August 22, 2006 and is headquartered in Milpitas, California. The Company is a clinical-stage biopharmaceutical company with a proprietary peptide technology platform focused on discovering and developing new chemical entities to address significant unmet medical needs. Protagonist Pty Ltd is a wholly-owned subsidiary located in Brisbane, Australia. The Company manages its operations as a single operating segment. Reverse Stock Split In July 2016, the Company’s board of directors approved an amendment to the Company’s amended and restated certificate of incorporation to effect a reverse split of the Company’s issued and outstanding common stock at a 1-for-14.5 ratio, which was effected on August 1, 2016. The par value and authorized shares of common stock and convertible preferred stock were not adjusted as a result of the reverse split. All issued and outstanding common stock, options to purchase common stock and per share amounts contained in the consolidated financial statements have been retroactively adjusted to reflect the reverse stock split for all periods presented. The consolidated financial statements have also been retroactively adjusted to reflect a proportional adjustment to the conversion ratio for each series of preferred stock in connection with the reverse stock split. Initial Public Offering On August 10, 2016, the Company’s registration statement on Form S-1 (File Nos. 333-212476 and 333-213071) relating to its initial public offering (“IPO”) of common stock became effective. The IPO closed on August 16, 2016 at which time the Company issued 7,500,000 shares of its common stock at a price of $12.00 per share. In addition, upon closing the IPO, all outstanding shares of the redeemable convertible preferred stock converted into 8,577,571 shares of common stock and there are no shares of redeemable convertible preferred stock outstanding. In September 2016, the Company issued an additional 252,972 shares of common stock at a price of $12.00 per share following the underwriters’ exercise of their option to purchase additional shares. The Company received an aggregate of $83.6 million in cash, net of underwriting discounts and commissions, and after deducting offering costs paid by the Company. Liquidity The Company has incurred net losses from operations since inception and has an accumulated deficit of $64.6 million as of December 31, 2016. The Company’s ultimate success depends on the outcome of its research and development activities. The Company expects to incur additional losses and negative cash flows for the foreseeable future and it anticipates the need to raise additional capital to fully implement its business plan. The Company intends to raise such capital through the issuance of additional equity and/or strategic alliances with partner companies. As of December 31, 2016, the Company had $87.7 million of cash, cash equivalents and available-for-sale securities and management believes the existing cash, cash equivalents and available-for-sale securities will be sufficient to meet the Company’s anticipated operating and capital expenditure requirements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Protagonist Pty Ltd and have been prepared in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP). All intercompany balances and transactions have been eliminated in consolidation. The financial statements of Protagonist Pty Ltd use the Australian dollar as the functional currency since the majority of expense transactions occur in such currency. Gains and losses from foreign currency transactions were not material for all periods presented. The re-measurement from Australian dollar to U.S. dollars is outlined below: a. Equity accounts, except for the change in retained earnings during the year, have been translated using historical exchange rates. b. All other Australian dollar denominated assets and liabilities as of December 31, 2016 and 2015 have been translated using the year-end exchange rate. c. The consolidated statements of operations have been translated at the weighted average exchange rates in effect during each year, except for depreciation, which has been translated at historical exchange rates. Foreign currency translation gains and losses are reported as a component of stockholders’ equity (deficit) in accumulated other comprehensive loss on the consolidated balance sheets. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to accruals for research and development activities, fair value of redeemable convertible preferred stock tranche liability, fair value of redeemable convertible preferred stock warrant liability, fair value of common stock, stock-based compensation and income taxes. Management bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. Actual results may differ from those estimates. Concentrations of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and available-for-sale securities. Substantially all the Company’s cash is held by one financial institution that management believes is of high credit quality. Such deposits may, at times, exceed federally insured limits. Cash Equivalents Cash equivalents that are readily convertible to cash are stated at cost, which approximates fair value. The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Cash equivalents consist of amounts invested in money market funds, commercial paper and government bonds. Restricted Cash Restricted cash consisted of cash balances primarily held as security in connection with the Company’s corporate credit card. Available-for-Sale Securities All marketable securities have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its marketable securities at the time of purchase and reevaluates such designation as of each balance sheet date. Short-term marketable securities have maturities less than 365 days as of the balance sheet date. Long-term marketable securities have maturities greater than 365 days as of the balance sheet date. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest income. The cost of securities sold is based on the specific-identification method. Interest on marketable securities is included in interest income. Fair Value of Financial Instruments Fair value accounting is applied for all financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including cash equivalents, accounts payable and accrued expenses and other payables approximate fair value due to their short term maturities. See Note 3. Fair Value Measurements regarding the fair value of the Company’s other financial assets and liabilities. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the consolidated balance sheet and any resulting gain or loss is reflected in operations in the period realized. Impairment of Long-Lived Assets The Company reviews long-lived assets, primarily comprised of property and equipment, for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future net cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There have been no such impairments of long-lived assets for any of the periods presented. Accrued Research and Development Costs The Company accrues for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of preclinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced, and include these costs in accrued expenses and other payables in the consolidated balance sheets and within research and development expense in the consolidated statements of operations. These costs are a significant component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its third-party service providers. The Company makes significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled, and the rate of patient enrollments may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. Comprehensive Loss Comprehensive loss represents all changes in stockholders’ equity (deficit) except those resulting from and distributions to stockholders. The Company’s foreign currency translation and unrealized gains and losses on available-for-sale securities represent the only components of other comprehensive loss that are excluded from the reported net loss and that are presented in the consolidated statements of comprehensive loss. Income Taxes The Company uses the asset and liability method to account for income taxes in accordance with the authoritative guidance for income taxes. Under this method, deferred tax assets and liabilities are determined based on future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, and tax loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest and penalties related to unrecognized tax benefits in income tax expense. To date, there have been no interest or penalties recorded in relation to the unrecognized tax benefits. Research and Development Costs Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to others that conduct certain research and development activities on the Company’s behalf. Research and Development Tax Incentive The Company is eligible under the AusIndustry research and development tax incentive program to obtain a cash amount from the Australian Taxation Office (“ATO”). The tax incentive is available to the Company on the basis of specific criteria with which the Company must comply. Specifically, the Company must have revenue of less than AUD 20.0 million and cannot be controlled by income tax exempt entities. These research and development tax incentives are recognized as contra research and development expense when the right to receive has been attained and funds are considered to be collectible. The tax incentive is denominated in Australian dollars and, therefore, the related receivable is remeasured into U.S. dollars as of each reporting date. Under certain conditions, research and development activities conducted outside Australia (“overseas finding”) also qualify for the research and development tax incentive. Funds received for overseas finding are at a risk of clawback until substantiation that less than 50% research and development expenditures for a project will be incurred overseas. A deferred tax incentive is recorded upon the cash receipt of the overseas finding funds and a reduction of research and development expenses is not recognized until the Company can substantiate that more than 50% of the total project expenditure will occur in Australia. When there is reasonable assurance that the grant will be received with remote risk of clawback, the relevant expenditure has been incurred, and the consideration can be reliably measured, the Company records the research and development incentive, including the overseas finding funds, as research and development tax incentive receivable and a reduction of research and development expenses for the balance to reflect that the funds are owed to the Company for the year the eligible costs are incurred. SBIR Grants The Company has been awarded Small Business Innovation Research (“SBIR”) grants from the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health (“NIH”) in support of its research activities. The Company records the eligible costs incurred under the SBIR grants as a reduction of research and development expenses. Redeemable Convertible Preferred Stock Tranche Liability The Company has determined that the Company’s obligation to issue additional shares of the Company’s redeemable convertible preferred stock represents a freestanding financial instrument, which was accounted for as a liability. The freestanding redeemable convertible preferred stock tranche liability was initially recorded at fair value, with fair value changes recognized in the consolidated statements of operations. At the time of the exercise or expiration of the option, any remaining value of the redeemable convertible preferred stock tranche liability is reclassified to redeemable convertible preferred stock with no further remeasurement required. Redeemable Convertible Preferred Stock Warrant Liability The Company has accounted for its freestanding warrants to purchase shares of the Company’s redeemable convertible preferred stock as liabilities at fair value upon issuance. At the end of each reporting period, changes in estimated fair value during the period are recorded in the consolidated statements of operations. The Company continued to adjust the warrant liability for changes in fair value until the earlier of the exercise of the warrants or expiration on May 10, 2016, and no further remeasurement is required . Stock-based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date using the Black-Scholes option-pricing model. Stock-based compensation expense is recognized over the requisite service period using the straight-line method and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Stock-based compensation expense for options granted to non-employees as consideration for services received is measured on the date of performance at the fair value of the consideration received or the fair value of the equity instruments issued, using the Black-Scholes option-pricing model, whichever can be more reliably measured. Compensation expense for options granted to non-employees is periodically remeasured as the underlying options vest. Net Loss per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period, without consideration of potentially dilutive securities. The net loss attributable to common stockholders is calculated by adjusting the net loss of the Company for the accretion on the redeemable convertible preferred stock. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders for all periods presented since the effect of potentially dilutive securities are anti-dilutive given the net loss of the Company. Recent Accounting Pronouncements In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties About an Entity’s Ability to Continue as a Going Concern In November 2015, FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes In February 2016, the FASB issued ASU No. 2016-02, Leases In March 2016, the FASB issued ASU 2016-09 Compensation-Stock Compensation (Topic 718) Improvements to Employee Share-Based Payment Accounting, which is intended to simplify several aspects of the accounting for employee share-based payment transactions, including the income tax consequences, the determination of forfeiture rates, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This ASU is effective for fiscal years and interim periods within those years beginning after December 15, 2016, and early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2016-09 will have on its consolidated financial statements and related disclosures. In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, Financial Instruments – Credit Losses (Topic 326) In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230) – Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230) – Restricted Cash,

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Financial assets and liabilities are recorded at fair value. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value and expands disclosures regarding fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows: Level 1 Level 2— Level 3 In determining fair value, the Company utilizes quoted market prices, broker or dealer quotation, or valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible as well as considers counterparty credit risk in its assessment of fair value. The following table presents the fair value of the Company’s financial assets and liabilities determined using the inputs defined above (amounts in thousands). December 31, 2016 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 11,270 $ — $ — $ 11,270 Corporate bonds — 21,841 — 21,841 Commercial paper — 10,769 — 10,769 Governmental bonds — 41,289 — 41,289 Total financial assets $ 11,270 $ 73,899 $ — $ 85,169 December 31, 2015 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 2,136 $ — $ — $ 2,136 Corporate bonds — 7,368 — 7,368 Commercial paper — 500 — 500 Total financial assets $ 2,136 $ 7,868 $ — $ 10,004 Liabilities: Redeemable convertible preferred stock tranche liability $ — $ — $ 1,643 $ 1,643 Redeemable convertible preferred stock warrant liability — — 480 480 Total financial liabilities $ — $ — $ 2,123 $ 2,123 The corporate bonds, commercial paper and government bonds are classified as Level 2 as they were valued based upon quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Level 3 instruments are valued based on unobservable inputs that are supported by little or no market activity and reflect the Company’s assumptions in measuring fair value. The fair value measurements of the redeemable convertible preferred stock tranche liability and the redeemable convertible preferred stock warrant liability were based on significant inputs not observed in the market and thus represent a Level 3 measurement. The redeemable convertible preferred stock tranche liability stems from the initial sale of the Company’s Series C redeemable convertible preferred stock wherein the Company was obligated to sell additional shares in subsequent closings contingent upon a majority of the stockholders of the outstanding redeemable convertible preferred stock and/or the achievement of certain development milestones. The subsequent closings were deemed to be freestanding financial instruments that were at the option of the holders. The Company estimated the fair value of this liability using a one-step binomial lattice model in combination with the Option Pricing Model. The change in fair value was recognized as a gain or loss in the consolidated statements of operations. See Note 10 for further discussion on the redeemable convertible preferred stock tranche liability and related valuations. The determination of the fair value of the redeemable convertible preferred stock warrant liability is discussed in Note 8. Generally, increases or decreases in the fair value of the underlying redeemable convertible preferred stock would result in a directionally similar impact in the fair value measurement of the warrant liability. The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial instruments as follows (in thousands): Year Ended December 31, 2016 2015 Redeemable Convertible Preferred Stock Tranche Liability: Beginning balance $ 1,643 $ — Issuance of Series C redeemable convertible preferred stock tranche liability — 1,017 Change in fair value upon revaluation 4,194 626 Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock (5,837 ) — Ending balance $ — $ 1,643 Year Ended December 31, 2016 2015 Redeemable Convertible Preferred Stock Warrant Liability: Beginning balance $ 480 $ 1,023 Change in fair value upon revaluation 525 (543 ) Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock (1,005 ) — Ending balance $ — $ 480

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	4. Balance Sheet Components Cash Equivalents and Available-for-sale Securities Cash equivalents and available-for-sale securities consisted of the following (in thousands): December 31, 2016 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 11,270 $ — $ — $ 11,270 Corporate bonds 21,886 — (45 ) 21,841 Commercial paper 10,769 — — 10,769 Government bonds 41,316 2 (29 ) 41,289 Total cash equivalents and available-for-sale securities $ 85,241 $ 2 $ (74 ) $ 85,169 Classified as: Cash equivalents $ 18,504 Available-for-sale securities - current 56,515 Available-for-sale securities - noncurrent 10,150 Total cash equivalents and available-for-sale securities $ 85,169 December 31, 2015 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 2,136 $ — $ — $ 2,136 Corporate bonds 7,373 — (5 ) 7,368 Commercial paper 500 — — 500 Total cash equivalents and available-for-sale securities $ 10,009 $ — $ (5 ) $ 10,004 Classified as: Cash equivalents $ 2,136 Available-for-sale securities - current 7,868 Total cash equivalents and available-for-sale securities $ 10,004 All available-for-sale securities - current held as of December 31, 2016 and December 31, 2015 had contractual maturities of less than one year. All available securities – noncurrent held as of December 31, 2016 had contractual maturities of greater than one year but less than two years. There have been no material realized gains or losses on available-for-sale securities for the periods presented. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2016 2015 Prepaid clinical and research related expenses $ 2,488 $ 1,253 Other 906 305 Prepaid expenses and other current assets $ 3,394 $ 1,558 Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): December 31, 2016 2015 Laboratory equipment $ 1,650 $ 1,452 Furniture and computer equipment 163 140 Leasehold improvements 62 48 Total property and equipment 1,875 1,640 Less: accumulated depreciation and amortization (1,313 ) (1,031 ) Property and equipment, net $ 562 $ 609 Depreciation expense for the years ended December 31, 2016, 2015 and 2014 was $317,000, $247,000 and $258,000, respectively. As of December 31, 2016 and 2015, $8,000 and $51,000, respectively, property and equipment, net, were located in Australia. The remainder of the assets are located in the United States. Accrued Expenses and Other Payables Accrued expenses and other payables consisted of the following (in thousands): December 31, 2016 2015 Accrued clinical and research related expenses $ 3,617 $ 976 Accrued employee related expenses 1,420 754 Other 235 149 Total accrued expenses and other payables $ 5,272 $ 1,879

Research Collaboration and Lice

Research Collaboration and License Agreement	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Research Collaboration and License Agreement	5. Research Collaboration and License Agreement In October 2013, the Company’s former collaboration partner decided to abandon a collaboration program with the Company and, pursuant to the terms of the agreement between the Company and the former collaboration partner, the Company elected to assume the responsibility for the development and commercialization of the product. Upon the former collaboration partner’s abandonment, it assigned to the Company certain intellectual property arising from the collaboration and also granted the Company an exclusive license to certain background intellectual property rights of the former collaboration partner that relate to the products assumed by the Company. Upon the nomination of PTG-300 as a development candidate, the Company owed the former collaboration partner a payment of $250,000. If the Company initiates a Phase 1 clinical trial for PTG-300, it will pay the former collaboration partner an additional $250,000. The Company has the right, but not the obligation, to further develop and commercialize the products and, if the Company successfully develops and commercializes PTG-300 without a partner, the Company will pay to the former collaboration partner up to an additional aggregate of $128.5 million for the achievement of certain development, regulatory and sales milestone events. In addition, the Company will pay to the former collaboration partner a low single digit royalty on worldwide net sales of the product until the later of ten years from the first commercial sale of the product or the expiration of the last patent covering the product. For the year ended December 31, 2016, the Company recorded research and development expense of $250,000 under this agreement. There were no such costs incurred for the years ended December 31, 2015 or 2014.

Government Programs

Government Programs	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Government Programs	6. Government Programs Research and Development Tax Incentive The Company recognized AUD 5.3 million ($4.0 million), AUD 978,000 ($736,000) and AUD 639,000 ($577,000) as a reduction of research and development expenses for the years ended December 31, 2016, 2015 and 2014, respectively, in connection with the research and development tax incentive from Australia. As of December 31, 2016 and December 31, 2015, the research and development tax incentive receivable was AUD 3.1 million ($2.2 million) and AUD 978,000 ($715,000), respectively. In March 2016, the Company received AUD 237,000 ($182,000) for overseas findings and recorded the funds as deferred tax incentive in accrued expenses and other payables on the consolidated balance sheet due to the possibility that the funds could have to be repaid. In October 2016, the Company received AUD 3.0 million ($2.2 million) including interest, in connection with the Australian research and development tax incentive. Of the funds received, AUD 1.0 million ($0.7 million) reduced the research and development tax incentive receivable and AUD 2.0 million ($1.5 million), which was for overseas findings, was recorded as deferred tax incentive in accrued expenses and other payables on the consolidated balance sheet due to the risk of clawback. In December 2016, the Company’s research and development project under the AusIndustry research and development tax incentive program was complete and the Company substantiated that more than 50% of the total project expenditures occurred in Australia. Therefore, the overseas finding related incentive amounts are not deemed to be at risk of clawback and the Company recognized AUD 2.2 million ($1.6 million) as a reduction of research and development expenses for the overseas findings received in 2016. SBIR Grant In September 2015, the Company was awarded a Phase 1 SBIR Grant from the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health (“NIH”) in support of research on orally stable peptide antagonists of the Interleukin-23 receptor (“IL-23R”) as potential treatments for inflammatory bowel diseases (“IBD”). The total grant award was $224,000 and is for the period from September 2015 to August 2016. In July 2016, the Company was awarded a Phase 1 SBIR Grant from the National Institute of Heart and Lung Diseases of the NIH in support of preclinical research aimed at discovering and optimizing lead molecules as novel peptide mimetics of the natural hepcidin hormone. The total grant award was $219,000 and is for the period from August 2016 to January 2017. The Company recognizes contra research and development when expenses related to the grants have been incurred and the grant funds become contractually due from NIH. The Company recorded $169,000 and $155,000 as a reduction of research and development expenses for the years ended December 31, 2016 and 2015, respectively. The Company recorded a receivable for $100,000 and $155,000 as of December 31, 2016 and 2015, respectively, to reflect the eligible costs incurred under the grants that are contractually due to the Company and such amounts are included in the prepaid expenses and other current assets on the consolidated balance sheets.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Lease Arrangements The Company leases its facility under a noncancelable operating lease that expires in April 2018. The Company has provided a security deposit of $30,000 as collateral for the lease, which is included in other assets on the consolidated balance sheets. The following table summarizes the Company’s future minimum lease payments as of December 31, 2016 (in thousands): Year Ending December 31: Amount 2017 $ 368 2018 87 Total $ 455 The Company’s rent expense was $408,000, $280,000 and $184,000 for the years ended December 31, 2016, 2015 and 2014, respectively. Rent expense is recognized on a straight-line basis over the term of the leases and accordingly, the Company records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Indemnifications In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by California corporate law. The Company currently has directors’ and officers’ insurance. To date, the Company has not incurred material costs to defend lawsuits or settle claims related to the indemnification agreements. The Company believes that the fair value of these indemnification agreements is minimal and has not accrued any amounts for the obligations.

Preferred Stock Warrants

Preferred Stock Warrants	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Preferred Stock Warrants	8. Preferred Stock Warrants In connection with the Series B redeemable convertible preferred stock financing, the Company issued warrants to purchase 4,000,000 shares of Series B redeemable convertible preferred stock at an exercise price of $0.01 per share. These warrants would become exercisable only when certain milestones were met on programs begun as a result of collaborations entered into in 2011 and 2012. In particular, 50% of the warrants would become exercisable upon the Company publicly announcing its first Investigational New Drug (“IND”) candidate to the extent such IND candidate was the result of, or related to, the Company’s previous collaboration(s) with Ironwood Pharmaceuticals and/or Zealand Pharma A/S, and the balance would become exercisable upon the first dosing of a human patient in a clinical trial that was the result of, or related to, the Company’s previous collaboration(s) with Ironwood Pharmaceuticals and/or Zealand Pharma A/S. In August 2013, the initial closing date for the Series B financing, the Company issued 2,000,000 of the warrants (“First Tranche Warrants”). On August 15, 2014, in connection with the closing of the Series B second tranche financing, the Company issued the balance of the warrants (“Second Tranche Warrants”). The fair value of the warrants outstanding as of December 31, 2015 was remeasured at $480,000, determined using a one-step binomial lattice model in combination with the Option Pricing Model and the following assumptions: risk-free interest rate of 0.90%, expected life of 1.6 years and expected volatility of 57.0% and probability of exercisability of 95% and 0% for the first tranche and second tranche, respectively. In March 2016, the Company made a public announcement related to a preclinical candidate which triggered the achievement of the milestone and warrants to purchase 2,000,000 shares of Series B redeemable convertible preferred stock became exercisable as of that date. In April 2016, 1,999,998 shares of Series B redeemable convertible preferred stock were issued for cash proceeds of $20,000 in connection with the exercise of warrants. Immediately prior to the exercise of the warrants, the fair value of the warrants was remeasured at $1.0 million, determined using a hybrid method of the Option Pricing Model with a 67% weighted value per share and the probability-weighted expected return method (“PWERM”) with a 33% weighted value per share. The following assumptions were used in the Option Pricing Model: risk-free interest rate of 0.73%, expected life of 2.0 years and expected volatility of 52.0%. The PWERM method included probabilities of three IPO scenarios occurring in July 2016. The scenarios were weighted based on the Company’s estimate of each event occurring in deriving the estimated fair value. Upon the exercise of warrants, the redeemable convertible preferred stock warrant liability of $1.0 million was reclassified to redeemable convertible preferred stock. In May 2016, the remaining warrants for the purchase of 2,000,000 shares of Series B redeemable convertible preferred stock expired unexercised. The Company recorded a charge of $525,000 and $872,000 for the years ended December 31, 2016 and 2014, respectively, representing the increase in the fair value of the redeemable convertible preferred stock warrant liability in the consolidated statements of operations. The Company recorded a gain of $543,000 for the year ended December 31, 2015, representing the decrease in the fair value of the redeemable convertible preferred stock warrant liability in the consolidated statements of operations.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Redeemable Convertible Preferred Stock	9. Redeemable Convertible Preferred Stock In April 2016, 1,999,998 shares of Series B redeemable convertible preferred stock were issued in connection with the exercise of warrants for cash proceeds of $20,000. Following the closing of the IPO, all outstanding shares of the redeemable convertible preferred stock converted into 8,577,571 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. There were no shares of redeemable convertible preferred stock outstanding as of December 31, 2016. The table below provides information on the Company’s redeemable convertible preferred stock as of December 31, 2015 (in thousands, except shares and original issue price): Shares Original Authorized Issued and Outstanding Carrying Value Aggregate Series A $ 1.00 6,037,500 6,037,500 $ 1,751 $ 6,038 Series B $ 0.50 40,000,000 36,000,000 18,825 18,000 Series C $ 0.4979 80,337,411 35,147,617 16,420 17,500 Total redeemable convertible preferred stock 126,374,911 77,185,117 $ 36,996 $ 41,538 As only the passage of time was required for Series A, B and C to become redeemable, the Company was accreting the carrying value of Series A, B and C to their redemption value over the period from the respective date of issuance to July 2022, (the earliest redemption date) up to the IPO date. In the event of a change of control of the Company, proceeds would be distributed in accordance with the liquidation preferences set forth in the Company’s Amended and Restated Certificate of Incorporation unless the holders of redeemable convertible preferred stock had converted their redeemable convertible preferred stock into shares of common stock. Therefore, redeemable convertible preferred stock was classified outside of stockholders’ equity (deficit) on the consolidated balance sheets, as Series A, B and C redeemable convertible preferred stock can be redeemed and as events triggering the liquidation preferences were not solely within the Company’s control. The Company recorded $558,000, $75,000, and $146,000 for the accretion of the redeemable convertible preferred stock during the years ended December 31, 2016, 2015, and 2014, respectively. The accretion was recorded as an offset to the additional paid in capital until such balance was depleted and any remaining accretion was recorded to accumulated deficit.

Redeemable Convertible Prefer18

Redeemable Convertible Preferred Stock Tranche Liability	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Redeemable Convertible Preferred Stock Tranche Liability	10. Redeemable Convertible Preferred Stock Tranche Liability In August 2014, the Company completed the closing of the Series B Second Tranche and issued 18,000,000 shares of Series B redeemable convertible preferred stock for gross cash proceeds of $9.0 million. At this time the Series B redeemable convertible preferred stock liability was remeasured at $2.3 million using a one-step binomial lattice model in combination with option pricing method based on the following assumptions: 100% probability of achievement of the development milestones, stock price of $0.50 per share, expected term of 0 years and risk-free rate of 0.5%. Upon the closing of the Series B Second Tranche, the Series B redeemable convertible preferred stock liability was terminated and the balance of the liability of $2.3 million was reclassified to redeemable convertible preferred stock. In July 2015, the Company entered into the Series C Preferred Stock Purchase Agreement (“the Series C Agreement”) for the issuance of up to 80,337,411 shares of Series C redeemable convertible preferred stock at a price of $0.4979 per share, in multiple closings. The initial closing occurred on July 10, 2015, whereby 35,147,617 shares of Series C redeemable convertible preferred stock were issued for gross proceeds of approximately $17.5 million. According to the initial terms of the Series C Agreement, the Company could issue 45,189,794 additional shares under the same terms as the initial closing, in a subsequent closing (“Series C Second Tranche”) contingent upon the achievement of certain development milestones. On the date of the initial closing, the Company recorded a Series C redeemable convertible preferred stock liability of $1.0 million, as the fair value of the obligation/right to complete the Series C Second Tranche. The fair value of the Series C redeemable convertible preferred stock liability on the date of the initial closing was determined using a one-step binomial lattice model in combination with the option pricing method based on the following assumptions: 90% probability of achievement of the development milestones, stock price of $0.4979 per share, expected term of 1.0 year, and risk-free rate of 0.5%. At December 31, 2015, the fair value of the Series C redeemable convertible preferred stock liability was remeasured and determined to be $1.6 million using a one-step binomial lattice model in combination with the Option Pricing Model based on the following assumptions: 95% probability of achievement of the development milestones, stock price of $0.4979 per share, expected term of 0.53 year, and risk-free rate of 0.9%. In March 2016, the Company completed the closing of the Series C Second Tranche and issued 45,189,794 shares of Series C redeemable convertible preferred stock for net cash proceeds of $22.5 million. At this time the Series C redeemable convertible preferred stock liability was remeasured at $5.8 million, determined using a hybrid method of the Option Pricing Model with a 67% weighted value per share and the PWERM with a 33% weighted value per share. The following assumptions were used in the Option Pricing Model: risk-free interest rate of 0.73%, expected life of 2.0 years and expected volatility of 52.0%. The PWERM method included probabilities of three IPO scenarios occurring in July 2016. The scenarios were weighted based on the Company’s estimate of each event occurring in deriving the estimated fair value. Upon the closing of the Series C Second Tranche, the Series C redeemable convertible preferred stock liability was terminated and the balance of the liability of $5.8 million was reclassified to redeemable convertible preferred stock. For the years ended December 31, 2016, 2015 and 2014, the Company recorded a charge of $4.2 million, $626,000 and $897,000, respectively, for the change in the fair value of the redeemable convertible preferred stock liability in the consolidated statements of operations.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Common Stock	11. Common Stock The Company had reserved shares of common stock for issuance, on an as-converted basis, as follows: December 31, 2016 2015 Redeemable convertible preferred stock outstanding — 5,323,103 Options issued and outstanding 2,393,829 833,178 Options available for future grants 164,328 147,219 Redeemable convertible preferred stock warrants — 275,861 Total 2,558,157 6,579,361

Equity Plans

Equity Plans	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Plans	12. Equity Plans Equity Incentive Plan In May 2007, the Company established its 2007 Stock Option and Incentive Plan (the “2007 Plan”) which provides for the granting of stock options to employees and consultants of the Company. Options granted under the 2007 Plan may be either incentive stock options (ISOs) or nonqualified stock options (NSOs). ISOs may be granted only to Company employees (including officers and directors who are also employees). NSOs may be granted to Company employees and consultants. Options under the 2007 Plan have a term of ten years and generally vest over a four-year period with one-year cliff vesting. In July 2016, the Company’s board of directors and stockholders approved the 2016 Equity Incentive Plan (the “2016 Plan”) to replace the 2007 Stock Option Plan and became effective upon the IPO. The 2016 Plan is administered by the Board of Directors or a committee appointed by the Board of Directors, which determines the types of awards to be granted, including the number of shares subject to the awards, the exercise price and the vesting schedule. Under the 2016 Plan, 1,200,000 shares of the Company’s common stock have been initially reserved for the issuance of stock options, restricted stock units and other awards to employees, directors and consultants. Options granted under the 2016 Plan expire no later than 10 years from the date of grant. The exercise price of each option may not be less than 100% of the fair market value of the common stock at the date of grant. Options may be granted to stockholders possessing more than 10% of the total combined voting power of all classes of stocks of the Company at an exercise price at least 110% of the fair value of the common stock at the date of grant and the options are not exercisable after the expiration of 10 years from the date of grant. Employee stock options generally vest 25% upon one year of continued service to the Company, with the remainder in monthly increments over three additional years. Upon adoption of the 2016 Plan, no additional stock awards will be issued under the 2007 Stock Option Plan. Options granted under the 2007 Stock Option Plan that were outstanding on the date the 2016 plan became effective remain subject to the terms of the 2007 Stock Option Plan. The number of options available for grant under the 2007 Plan was ceased and the number was added to the common stock reserved for issuance under the 2016 Plan. As of December 31, 2016, the Company has reserved 1,200,000 shares of common stock for issuance under the 2016 Plan. Stock Options Activity under the Company’s equity incentive plans is set forth below: Options Outstanding Options Options Weighted- Average Weighted- Average Aggregate (in thousands) Balances at December 31, 2013 70,082 284,879 $ 1.10 7.92 Additional options authorized 240,425 — Options granted (199,519 ) 199,519 1.83 Options exercised — (2,548 ) 1.30 Options forfeited 5,844 (5,844 ) 1.13 Balances at December 31, 2014 116,832 476,006 1.40 8.04 Additional options authorized 431,411 — Options granted (408,623 ) 408,623 1.24 Options exercised — (43,852 ) 1.30 Options forfeited 7,599 (7,599 ) 1.40 Balances at December 31, 2015 147,219 833,178 1.33 8.56 Additional options authorized 1,697,088 — Options granted (1,679,979 ) 1,679,979 14.24 Options exercised — (119,328 ) 1.28 Balances at December 31, 2016 164,328 2,393,829 $ 10.39 8.79 $ 27,820 Options exercisable – December 31, 2016 492,714 $ 5.19 7.70 $ 8,286 Options vested and expected to vest – December 31, 2016 2,369,135 $ 10.37 8.79 $ 27,596 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock on December 31, 2016. The aggregate intrinsic value of options exercised was $169,000 for the year ended December 31, 2016. The aggregate intrinsic value of options exercised was immaterial for the years ended December 31, 2015 and 2014, respectively. During the years ended December 31, 2016, 2015, and 2014 the estimated weighted-average grant-date fair value of common stock underlying options granted was $8.20, $0.69, and $0.82 per share, respectively. Employee Stock Options Valuation The fair value of employee and director stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2016 2015 2014 Expected term (in years) 4.16 – 5.95 5.89 6.08 Expected volatility 62.5 – 64.8 % 59.8 % 64.7 % Risk-free interest rate 1.27 – 1.79 % 1.57 – 1.58 % 1.89 % Dividend yield — — — Prior to the completion of the Company’s IPO, the fair value of the Company’s shares of common stock underlying its stock options had historically been determined by the Company’s Board of Directors. Because there had been no public market for the Company’s common stock prior to August 2016, the Company’s Board of Directors had determined fair value of the common stock at the time of grant of the option by considering a number of objective and subjective factors including important developments in the Company’s operations, valuations performed by an independent third party, sales of redeemable convertible preferred stock, actual operating results and financial performance, the conditions in the biotechnology industry and the economy in general, the stock price performance and volatility of comparable public companies, and the lack of liquidity of the Company’s common stock, among other factors. For stock options granted after the completion of the IPO, the Company’s Board of Directors determined the fair value of each share of underlying common stock based on the closing price of the Company’s common stock as reported on the date of grant. In determining the fair value of the options granted, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine. Expected Term Expected Volatility Risk-Free Interest Rate Expected Dividend Stock Options Granted to Non-employees Stock-based compensation related to stock options granted to non-employees is recognized as the stock options are earned. The fair value of the stock options granted was calculated at each reporting date using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2016 2015 2014 Expected term (in years) 6.59 –9.97 6.8 9.4 Expected volatility 62.5 – 62.8 % 59.8 % 64.7 % Risk-free interest rate 1.29 – 1.79 % 1.95 % 2.34 % Dividend yield — — — During the years ended December 31, 2016, 2015, and 2014 the Company granted 59,647, 4,816, and 11,805 shares, respectively, to non-employee consultants. The Company recorded stock-based compensation expense during the years ended December 31, 2016, 2015, and 2014 of $505,000, $15,000, and $5,000, respectively. Employee Stock Purchase Plan In July 2016, the Company’s board of directors and stockholders approved the 2016 Employee Stock Purchase Plan (the “2016 ESPP”), which became effective upon the IPO. The 2016 ESPP is intended to qualify as an employee stock purchase plan under Section 423 of the Internal Revenue Code of 1986, as amended, and is administered by the Company’s board of directors and the Compensation Committee of the board of directors. Under the 2016 ESPP, 150,000 shares of the Company’s common stock have been initially reserved for employee purchases of the Company’s common stock, with an automatic annual increase to the shares issuable under the 2016 ESPP on the first day of each fiscal year for a period of up to 10 years in an amount equal to (i) the lesser of 1% of the total number of shares of common stock outstanding on December 31 of the preceding fiscal year and 300,000 shares of the Company’s common stock, or (ii) a lower number determined by the Board of Directors. The 2016 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation. At the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock at the beginning of the offering period or at the end of each applicable purchase period. The fair value of the rights granted under the 2016 ESPP was calculated using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2016 Expected term (in years) 0.60 Expected volatility 52.48 % Risk-free interest rate 0.45 % Dividend yield — Stock-Based Compensation Total stock-based compensation expense recognized for both employees and non-employees for stock options and the 2016 ESPP was as follows (in thousands): Year Ended December 31, 2016 2015 2014 Research and development $ 1,080 $ 39 $ 17 General and administrative 1,050 60 25 Total stock-based compensation expense $ 2,130 $ 99 $ 42 As of December 31, 2016 there was $12.6 million of total unrecognized stock-based compensation costs related to stock options that the Company expects to recognize over a period of approximately 3.12 years.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
401(k) Plan	13. 401(k) Plan In March 2012, the Company adopted a retirement and savings plan under Section of 401(k) of Internal Revenue Code (the 401(k) Plan) covering all employees. The 401(k) Plan allows employees to make pre- and post-tax contributions up to the maximum allowable amount set by the IRS. The Company does not make matching contributions to the 401(k) plan on behalf of participants.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes No provision for income taxes was recorded for the years ended December 31, 2016, 2015 and 2014. The Company has incurred net operating losses for all the periods presented. The Company has not reflected any benefit of such net operating loss carryforwards in the consolidated financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets. The following table presents domestic and foreign components of net loss for the periods presented (in thousands): Year Ended December 31, 2016 2015 2014 Domestic $ (34,977 ) $ (10,483 ) $ (9,515 ) Foreign (2,200 ) (4,375 ) (1,557 ) Total net loss $ (37,177 ) $ (14,858 ) $ (11,072 ) The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Year Ended December 31, 2016 2015 2014 Federal statutory income tax rate 34.0 % 34.0 % 34.0 % State taxes, net of federal benefit 6.5 (2.7 ) 4.1 Warrant revaluation (4.3 ) (0.2 ) (5.5 ) Foreign tax rate difference (1.6 ) (11.8 ) (6.8 ) Change in valuation allowance (36.0 ) (19.9 ) (26.5 ) Other 1.4 0.6 0.7 Provision for income taxes 0.0 % 0.0 % 0.0 % The components of the deferred tax assets are as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 21,501 $ 9,513 Depreciation and amortization 419 480 Accruals/other 908 293 Research and development credits & foreign credits 1,143 285 Total deferred tax assets 23,971 10,571 Valuation allowance (23,971 ) (10,571 ) Net deferred tax assets $ — $ — Realization of the deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. The Company has established a valuation allowance to offset deferred tax assets as of December 31, 2016 and 2015 due to the uncertainty of realizing future tax benefits from its net operating loss carryforwards and other deferred tax assets. The valuation allowance increased by approximately $13.4 million, $3.0 million and $2.9 million during the year ended December 31, 2016, 2015 and 2014, respectively. The increase in the valuation allowance is mainly related to the increase in net operating loss carryforwards incurred during the respective taxable years. At December 31, 2016, the Company had net operating loss carryforwards for federal income tax purposes of approximately $48.0 million which are available to offset future taxable income, if any, through 2033 and net operating loss carryforwards for state income tax purposes of approximately $37.7 million which are available to offset future taxable income, if any, through 2033. At December 31, 2016 the Company also had accumulated Australian tax losses of $9.2 million available for carry forward against future earnings which, under relevant tax laws, do not expire but may not be available under certain circumstances. As of December 31, 2016, the Company also had $1.1 million of federal and $0.6 million of state research and development tax credit carryforwards available to reduce future income taxes. The federal research and development tax credits will begin to expire in 2035, if not utilized. The state research and development tax credits have no expiration date. Federal and state laws impose substantial restrictions on the utilization of net operating loss and tax credit carryforwards in the event of an ownership change for tax purposes, as defined in Section 382 of the Internal Revenue Code. As a result of such ownership changes, the Company’s ability to realize the potential future benefit of tax losses and tax credits that existed at the time of the ownership change may be significantly reduced. The Company’s deferred tax asset and related valuation allowance would be reduced as a result. It is the Company’s policy to include penalties and interest expense related to income taxes as a component of other expense, as necessary. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2016 2015 2014 Balance at beginning of year $ 805 $ — $ — Additions based on tax positions related to in prior years 707 690 — Additions based on tax positions related to current year 619 115 — Balance at end of year $ 2,131 $ 805 $ — The Company does not expect that its uncertain tax positions will materially change in the next twelve months. The reversal of the uncertain tax benefits would not impact the Company’s effective tax rate as the Company continues to maintain a full valuation allowance against its deferred tax assets. The Company files income tax returns in the United States federal jurisdiction, the State of California and Australia. The Company is not currently under examination by income tax authorities in federal, state or other jurisdictions. The Company’s tax returns for 2012 through 2016 remain open for examination due to the carryover of unused net operating losses and tax credits.

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders	15. Net Loss per Share Attributable to Common Stockholders As the Company had net losses for the years ended December 31, 2016, 2015 and 2014, all potential common shares were determined to be anti-dilutive. The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2016 2015 2014 Numerator: Net loss $ (37,177 ) $ (14,858 ) $ (11,072 ) Accretion of redeemable convertible preferred stock (558 ) (75 ) (146 ) Net loss attributable to common stockholders $ (37,735 ) $ (14,933 ) $ (11,218 ) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 6,501,796 251,717 227,197 Net loss per share attributable to common stockholders, basic and diluted $ (5.80 ) $ (59.32 ) $ (49.38 ) The following outstanding shares of potentially dilutive securities have been excluded from diluted net loss per share calculations for the years ended December 31, 2016, 2015 and 2014, because their inclusion would be anti-dilutive: Year Ended December 31, 2016 2015 2014 Redeemable convertible preferred stock on an as-converted basis — 5,323,103 2,899,134 Options to purchase common stock 2,393,829 833,178 476,006 Warrants to purchase redeemable convertible preferred stock on an as-converted basis — 275,861 275,861 Total 2,393,829 6,432,142 3,651,001

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	16. Subsequent Events In March 2017, the Company entered into a lease agreement for a new office and laboratory space in Newark, California to relocate its operations to a larger facility. The lease commencement date is July 1, 2017 and the lease expires on June 30, 2024. The Company aggregate minimum lease payments totaling $13.4 million under the lease agreement and will provide the landlord with a letter of credit as the security deposit of $450,000.

Supplementary Financial Data (u

Supplementary Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Supplementary Financial Data (unaudited)	17. Supplementary Financial Data (unaudited) The following table presents the selected quarterly financial data for the years ended December 31, 2016 and 2015: Consolidated Statements of Operations Quarter Ended March 31 June 30 September 30 December 31 (In thousands, except per share amounts) 2016 Loss from operations $ (7,040 ) $ (7,091 ) $ (7,138 ) $ (11,397 ) Net loss $ (11,747 ) $ (7,098 ) $ (7,084 ) $ (11,248 ) Net loss per share of common stock attributable to common stockholders, basic and diluted $ (40.96 ) $ (19.07 ) $ (0.87 ) $ (0.67 ) 2015 Loss from operations $ (2,689 ) $ (3,083 ) $ (4,021 ) $ (5,001 ) Net loss $ (2,697 ) $ (3,219 ) $ (3,449 ) $ (5,493 ) Net loss per share of common stock attributable to common stockholders, basic and diluted $ (11.75 ) $ (13.78 ) $ (12.79 ) $ (20.31 )

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Protagonist Pty Ltd and have been prepared in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP). All intercompany balances and transactions have been eliminated in consolidation. The financial statements of Protagonist Pty Ltd use the Australian dollar as the functional currency since the majority of expense transactions occur in such currency. Gains and losses from foreign currency transactions were not material for all periods presented. The re-measurement from Australian dollar to U.S. dollars is outlined below: a. Equity accounts, except for the change in retained earnings during the year, have been translated using historical exchange rates. b. All other Australian dollar denominated assets and liabilities as of December 31, 2016 and 2015 have been translated using the year-end exchange rate. c. The consolidated statements of operations have been translated at the weighted average exchange rates in effect during each year, except for depreciation, which has been translated at historical exchange rates. Foreign currency translation gains and losses are reported as a component of stockholders’ equity (deficit) in accumulated other comprehensive loss on the consolidated balance sheets.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to accruals for research and development activities, fair value of redeemable convertible preferred stock tranche liability, fair value of redeemable convertible preferred stock warrant liability, fair value of common stock, stock-based compensation and income taxes. Management bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. Actual results may differ from those estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and available-for-sale securities. Substantially all the Company’s cash is held by one financial institution that management believes is of high credit quality. Such deposits may, at times, exceed federally insured limits.
Cash Equivalents	Cash Equivalents Cash equivalents that are readily convertible to cash are stated at cost, which approximates fair value. The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Cash equivalents consist of amounts invested in money market funds, commercial paper and government bonds.
Restricted Cash	Restricted Cash Restricted cash consisted of cash balances primarily held as security in connection with the Company’s corporate credit card.
Available-for-Sale Securities	Available-for-Sale Securities All marketable securities have been classified as “available-for-sale” and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its marketable securities at the time of purchase and reevaluates such designation as of each balance sheet date. Short-term marketable securities have maturities less than 365 days as of the balance sheet date. Long-term marketable securities have maturities greater than 365 days as of the balance sheet date. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest income. The cost of securities sold is based on the specific-identification method. Interest on marketable securities is included in interest income.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value accounting is applied for all financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including cash equivalents, accounts payable and accrued expenses and other payables approximate fair value due to their short term maturities. See Note 3. Fair Value Measurements regarding the fair value of the Company’s other financial assets and liabilities.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful lives of the assets. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the consolidated balance sheet and any resulting gain or loss is reflected in operations in the period realized.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, primarily comprised of property and equipment, for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future net cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There have been no such impairments of long-lived assets for any of the periods presented.
Accrued Research and Development Costs	Accrued Research and Development Costs The Company accrues for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of preclinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided but not yet invoiced, and include these costs in accrued expenses and other payables in the consolidated balance sheets and within research and development expense in the consolidated statements of operations. These costs are a significant component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed and in accordance with agreements established with its third-party service providers. The Company makes significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled, and the rate of patient enrollments may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect the Company’s results of operations.
Comprehensive Loss	Comprehensive Loss Comprehensive loss represents all changes in stockholders’ equity (deficit) except those resulting from and distributions to stockholders. The Company’s foreign currency translation and unrealized gains and losses on available-for-sale securities represent the only components of other comprehensive loss that are excluded from the reported net loss and that are presented in the consolidated statements of comprehensive loss.
Income Taxes	Income Taxes The Company uses the asset and liability method to account for income taxes in accordance with the authoritative guidance for income taxes. Under this method, deferred tax assets and liabilities are determined based on future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases, and tax loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest and penalties related to unrecognized tax benefits in income tax expense. To date, there have been no interest or penalties recorded in relation to the unrecognized tax benefits.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to others that conduct certain research and development activities on the Company’s behalf.
Research and Development Tax Incentive	Research and Development Tax Incentive The Company is eligible under the AusIndustry research and development tax incentive program to obtain a cash amount from the Australian Taxation Office (“ATO”). The tax incentive is available to the Company on the basis of specific criteria with which the Company must comply. Specifically, the Company must have revenue of less than AUD 20.0 million and cannot be controlled by income tax exempt entities. These research and development tax incentives are recognized as contra research and development expense when the right to receive has been attained and funds are considered to be collectible. The tax incentive is denominated in Australian dollars and, therefore, the related receivable is remeasured into U.S. dollars as of each reporting date. Under certain conditions, research and development activities conducted outside Australia (“overseas finding”) also qualify for the research and development tax incentive. Funds received for overseas finding are at a risk of clawback until substantiation that less than 50% research and development expenditures for a project will be incurred overseas. A deferred tax incentive is recorded upon the cash receipt of the overseas finding funds and a reduction of research and development expenses is not recognized until the Company can substantiate that more than 50% of the total project expenditure will occur in Australia. When there is reasonable assurance that the grant will be received with remote risk of clawback, the relevant expenditure has been incurred, and the consideration can be reliably measured, the Company records the research and development incentive, including the overseas finding funds, as research and development tax incentive receivable and a reduction of research and development expenses for the balance to reflect that the funds are owed to the Company for the year the eligible costs are incurred.
SBIR Grants	SBIR Grants The Company has been awarded Small Business Innovation Research (“SBIR”) grants from the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health (“NIH”) in support of its research activities. The Company records the eligible costs incurred under the SBIR grants as a reduction of research and development expenses.
Redeemable Convertible Preferred Stock Tranche Liability	Redeemable Convertible Preferred Stock Tranche Liability The Company has determined that the Company’s obligation to issue additional shares of the Company’s redeemable convertible preferred stock represents a freestanding financial instrument, which was accounted for as a liability. The freestanding redeemable convertible preferred stock tranche liability was initially recorded at fair value, with fair value changes recognized in the consolidated statements of operations. At the time of the exercise or expiration of the option, any remaining value of the redeemable convertible preferred stock tranche liability is reclassified to redeemable convertible preferred stock with no further remeasurement required.
Redeemable Convertible Preferred Stock Warrant Liability	Redeemable Convertible Preferred Stock Warrant Liability The Company has accounted for its freestanding warrants to purchase shares of the Company’s redeemable convertible preferred stock as liabilities at fair value upon issuance. At the end of each reporting period, changes in estimated fair value during the period are recorded in the consolidated statements of operations. The Company continued to adjust the warrant liability for changes in fair value until the earlier of the exercise of the warrants or expiration on May 10, 2016, and no further remeasurement is required .
Stock-based Compensation	Stock-based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date using the Black-Scholes option-pricing model. Stock-based compensation expense is recognized over the requisite service period using the straight-line method and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Stock-based compensation expense for options granted to non-employees as consideration for services received is measured on the date of performance at the fair value of the consideration received or the fair value of the equity instruments issued, using the Black-Scholes option-pricing model, whichever can be more reliably measured. Compensation expense for options granted to non-employees is periodically remeasured as the underlying options vest.
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period, without consideration of potentially dilutive securities. The net loss attributable to common stockholders is calculated by adjusting the net loss of the Company for the accretion on the redeemable convertible preferred stock. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders for all periods presented since the effect of potentially dilutive securities are anti-dilutive given the net loss of the Company.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties About an Entity’s Ability to Continue as a Going Concern In November 2015, FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes In February 2016, the FASB issued ASU No. 2016-02, Leases In March 2016, the FASB issued ASU 2016-09 Compensation-Stock Compensation (Topic 718) Improvements to Employee Share-Based Payment Accounting, which is intended to simplify several aspects of the accounting for employee share-based payment transactions, including the income tax consequences, the determination of forfeiture rates, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This ASU is effective for fiscal years and interim periods within those years beginning after December 15, 2016, and early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2016-09 will have on its consolidated financial statements and related disclosures. In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, Financial Instruments – Credit Losses (Topic 326) In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230) – Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230) – Restricted Cash,
Fair Value Measurements	The redeemable convertible preferred stock tranche liability stems from the initial sale of the Company’s Series C redeemable convertible preferred stock wherein the Company was obligated to sell additional shares in subsequent closings contingent upon a majority of the stockholders of the outstanding redeemable convertible preferred stock and/or the achievement of certain development milestones. The subsequent closings were deemed to be freestanding financial instruments that were at the option of the holders. The Company estimated the fair value of this liability using a one-step binomial lattice model in combination with the Option Pricing Model. The change in fair value was recognized as a gain or loss in the consolidated statements of operations. See Note 10 for further discussion on the redeemable convertible preferred stock tranche liability and related valuations. The determination of the fair value of the redeemable convertible preferred stock warrant liability is discussed in Note 8. Generally, increases or decreases in the fair value of the underlying redeemable convertible preferred stock would result in a directionally similar impact in the fair value measurement of the warrant liability.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value	The following table presents the fair value of the Company’s financial assets and liabilities determined using the inputs defined above (amounts in thousands). December 31, 2016 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 11,270 $ — $ — $ 11,270 Corporate bonds — 21,841 — 21,841 Commercial paper — 10,769 — 10,769 Governmental bonds — 41,289 — 41,289 Total financial assets $ 11,270 $ 73,899 $ — $ 85,169 December 31, 2015 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 2,136 $ — $ — $ 2,136 Corporate bonds — 7,368 — 7,368 Commercial paper — 500 — 500 Total financial assets $ 2,136 $ 7,868 $ — $ 10,004 Liabilities: Redeemable convertible preferred stock tranche liability $ — $ — $ 1,643 $ 1,643 Redeemable convertible preferred stock warrant liability — — 480 480 Total financial liabilities $ — $ — $ 2,123 $ 2,123
Summary of Changes in Fair Value of Company's Level 3 Financial Instruments	The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial instruments as follows (in thousands): Year Ended December 31, 2016 2015 Redeemable Convertible Preferred Stock Tranche Liability: Beginning balance $ 1,643 $ — Issuance of Series C redeemable convertible preferred stock tranche liability — 1,017 Change in fair value upon revaluation 4,194 626 Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock (5,837 ) — Ending balance $ — $ 1,643 Year Ended December 31, 2016 2015 Redeemable Convertible Preferred Stock Warrant Liability: Beginning balance $ 480 $ 1,023 Change in fair value upon revaluation 525 (543 ) Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock (1,005 ) — Ending balance $ — $ 480

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Cash Equivalents and Available-for-sale Securities	Cash equivalents and available-for-sale securities consisted of the following (in thousands): December 31, 2016 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 11,270 $ — $ — $ 11,270 Corporate bonds 21,886 — (45 ) 21,841 Commercial paper 10,769 — — 10,769 Government bonds 41,316 2 (29 ) 41,289 Total cash equivalents and available-for-sale securities $ 85,241 $ 2 $ (74 ) $ 85,169 Classified as: Cash equivalents $ 18,504 Available-for-sale securities - current 56,515 Available-for-sale securities - noncurrent 10,150 Total cash equivalents and available-for-sale securities $ 85,169 December 31, 2015 Amortized Gross Unrealized Cost Gains Losses Fair Value Money market funds $ 2,136 $ — $ — $ 2,136 Corporate bonds 7,373 — (5 ) 7,368 Commercial paper 500 — — 500 Total cash equivalents and available-for-sale securities $ 10,009 $ — $ (5 ) $ 10,004 Classified as: Cash equivalents $ 2,136 Available-for-sale securities - current 7,868 Total cash equivalents and available-for-sale securities $ 10,004
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2016 2015 Prepaid clinical and research related expenses $ 2,488 $ 1,253 Other 906 305 Prepaid expenses and other current assets $ 3,394 $ 1,558
Summary of Property and Equipment Net	Property and equipment, net consisted of the following (in thousands): December 31, 2016 2015 Laboratory equipment $ 1,650 $ 1,452 Furniture and computer equipment 163 140 Leasehold improvements 62 48 Total property and equipment 1,875 1,640 Less: accumulated depreciation and amortization (1,313 ) (1,031 ) Property and equipment, net $ 562 $ 609
Summary of Accrued Expenses and Other Payables	Accrued expenses and other payables consisted of the following (in thousands): December 31, 2016 2015 Accrued clinical and research related expenses $ 3,617 $ 976 Accrued employee related expenses 1,420 754 Other 235 149 Total accrued expenses and other payables $ 5,272 $ 1,879

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Summary of Future Minimum Lease Payments	The following table summarizes the Company’s future minimum lease payments as of December 31, 2016 (in thousands): Year Ending December 31: Amount 2017 $ 368 2018 87 Total $ 455

Redeemable Convertible Prefer30

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Summary of Redeemable Convertible Preferred Stock	The table below provides information on the Company’s redeemable convertible preferred stock as of December 31, 2015 (in thousands, except shares and original issue price): Shares Original Authorized Issued and Outstanding Carrying Value Aggregate Series A $ 1.00 6,037,500 6,037,500 $ 1,751 $ 6,038 Series B $ 0.50 40,000,000 36,000,000 18,825 18,000 Series C $ 0.4979 80,337,411 35,147,617 16,420 17,500 Total redeemable convertible preferred stock 126,374,911 77,185,117 $ 36,996 $ 41,538

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Common Stock Reserved for Issuance	The Company had reserved shares of common stock for issuance, on an as-converted basis, as follows: December 31, 2016 2015 Redeemable convertible preferred stock outstanding — 5,323,103 Options issued and outstanding 2,393,829 833,178 Options available for future grants 164,328 147,219 Redeemable convertible preferred stock warrants — 275,861 Total 2,558,157 6,579,361

Equity Plans (Tables)

Equity Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Activity under Equity Incentive Plans	Activity under the Company’s equity incentive plans is set forth below: Options Outstanding Options Options Weighted- Average Weighted- Average Aggregate (in thousands) Balances at December 31, 2013 70,082 284,879 $ 1.10 7.92 Additional options authorized 240,425 — Options granted (199,519 ) 199,519 1.83 Options exercised — (2,548 ) 1.30 Options forfeited 5,844 (5,844 ) 1.13 Balances at December 31, 2014 116,832 476,006 1.40 8.04 Additional options authorized 431,411 — Options granted (408,623 ) 408,623 1.24 Options exercised — (43,852 ) 1.30 Options forfeited 7,599 (7,599 ) 1.40 Balances at December 31, 2015 147,219 833,178 1.33 8.56 Additional options authorized 1,697,088 — Options granted (1,679,979 ) 1,679,979 14.24 Options exercised — (119,328 ) 1.28 Balances at December 31, 2016 164,328 2,393,829 $ 10.39 8.79 $ 27,820 Options exercisable – December 31, 2016 492,714 $ 5.19 7.70 $ 8,286 Options vested and expected to vest – December 31, 2016 2,369,135 $ 10.37 8.79 $ 27,596
Schedule of Stock-based Compensation Expense for Employees and Non-employees for Stock Options and the 2016 ESPP	Total stock-based compensation expense recognized for both employees and non-employees for stock options and the 2016 ESPP was as follows (in thousands): Year Ended December 31, 2016 2015 2014 Research and development $ 1,080 $ 39 $ 17 General and administrative 1,050 60 25 Total stock-based compensation expense $ 2,130 $ 99 $ 42
Employee and Director [Member]
Schedule of Grant-date Fair Value of Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions	The fair value of employee and director stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2016 2015 2014 Expected term (in years) 4.16 – 5.95 5.89 6.08 Expected volatility 62.5 – 64.8 % 59.8 % 64.7 % Risk-free interest rate 1.27 – 1.79 % 1.57 – 1.58 % 1.89 % Dividend yield — — —
Non-employees [Member]
Schedule of Grant-date Fair Value of Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions	The fair value of the stock options granted was calculated at each reporting date using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2016 2015 2014 Expected term (in years) 6.59 –9.97 6.8 9.4 Expected volatility 62.5 – 62.8 % 59.8 % 64.7 % Risk-free interest rate 1.29 – 1.79 % 1.95 % 2.34 % Dividend yield — — —
2016 Employee Stock Purchase Plan [Member]
Schedule of Grant-date Fair Value of Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions	The fair value of the rights granted under the 2016 ESPP was calculated using the Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2016 Expected term (in years) 0.60 Expected volatility 52.48 % Risk-free interest rate 0.45 % Dividend yield —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic and Foreign Components of Net Loss	The following table presents domestic and foreign components of net loss for the periods presented (in thousands): Year Ended December 31, 2016 2015 2014 Domestic $ (34,977 ) $ (10,483 ) $ (9,515 ) Foreign (2,200 ) (4,375 ) (1,557 ) Total net loss $ (37,177 ) $ (14,858 ) $ (11,072 )
Summary of Effective Tax Rate of Provision For Income Taxes Differs From Federal Statutory Rate	The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Year Ended December 31, 2016 2015 2014 Federal statutory income tax rate 34.0 % 34.0 % 34.0 % State taxes, net of federal benefit 6.5 (2.7 ) 4.1 Warrant revaluation (4.3 ) (0.2 ) (5.5 ) Foreign tax rate difference (1.6 ) (11.8 ) (6.8 ) Change in valuation allowance (36.0 ) (19.9 ) (26.5 ) Other 1.4 0.6 0.7 Provision for income taxes 0.0 % 0.0 % 0.0 %
Components of Deferred Tax Assets	The components of the deferred tax assets are as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 21,501 $ 9,513 Depreciation and amortization 419 480 Accruals/other 908 293 Research and development credits & foreign credits 1,143 285 Total deferred tax assets 23,971 10,571 Valuation allowance (23,971 ) (10,571 ) Net deferred tax assets $ — $ —
Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): Year Ended December 31, 2016 2015 2014 Balance at beginning of year $ 805 $ — $ — Additions based on tax positions related to in prior years 707 690 — Additions based on tax positions related to current year 619 115 — Balance at end of year $ 2,131 $ 805 $ —

Net Loss per Share Attributab34

Net Loss per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2016 2015 2014 Numerator: Net loss $ (37,177 ) $ (14,858 ) $ (11,072 ) Accretion of redeemable convertible preferred stock (558 ) (75 ) (146 ) Net loss attributable to common stockholders $ (37,735 ) $ (14,933 ) $ (11,218 ) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 6,501,796 251,717 227,197 Net loss per share attributable to common stockholders, basic and diluted $ (5.80 ) $ (59.32 ) $ (49.38 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The following outstanding shares of potentially dilutive securities have been excluded from diluted net loss per share calculations for the years ended December 31, 2016, 2015 and 2014, because their inclusion would be anti-dilutive: Year Ended December 31, 2016 2015 2014 Redeemable convertible preferred stock on an as-converted basis — 5,323,103 2,899,134 Options to purchase common stock 2,393,829 833,178 476,006 Warrants to purchase redeemable convertible preferred stock on an as-converted basis — 275,861 275,861 Total 2,393,829 6,432,142 3,651,001

Supplementary Financial Data 35

Supplementary Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Selected Quarterly Financial Data	The following table presents the selected quarterly financial data for the years ended December 31, 2016 and 2015: Consolidated Statements of Operations Quarter Ended March 31 June 30 September 30 December 31 (In thousands, except per share amounts) 2016 Loss from operations $ (7,040 ) $ (7,091 ) $ (7,138 ) $ (11,397 ) Net loss $ (11,747 ) $ (7,098 ) $ (7,084 ) $ (11,248 ) Net loss per share of common stock attributable to common stockholders, basic and diluted $ (40.96 ) $ (19.07 ) $ (0.87 ) $ (0.67 ) 2015 Loss from operations $ (2,689 ) $ (3,083 ) $ (4,021 ) $ (5,001 ) Net loss $ (2,697 ) $ (3,219 ) $ (3,449 ) $ (5,493 ) Net loss per share of common stock attributable to common stockholders, basic and diluted $ (11.75 ) $ (13.78 ) $ (12.79 ) $ (20.31 )

Organization and Description 36

Organization and Description of Business - Additional Information (Detail) $ / shares in Units, $ in Thousands	Sep. 30, 2016USD ($)$ / sharesshares	Aug. 16, 2016$ / sharesshares	Jul. 31, 2016	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014shares	Dec. 31, 2013shares
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Reverse stock split description				In July 2016, the Company's board of directors approved an amendment to the Company's amended and restated certificate of incorporation to effect a reverse split of the Company's issued and outstanding common stock at a 1-for-14.5 ratio, which was effected on August 1, 2016.
Reverse stock split effective date				Aug. 1, 2016
Reverse stock split ratio			0.06896
Proceeds from stock issuance, net of underwriting discounts, commissions | $				$ 83,648
Number of shares converted		8,577,571
Preferred stock outstanding				0	77,185,117
Accumulated deficit | $				$ (64,593)	$ (27,416)
Cash, cash equivalents and available-for-sale securities | $				$ 87,700
Common Stock [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock issued				7,752,972
Initial Public Offering [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from stock issuance, net of underwriting discounts, commissions | $	$ 83,600
Common stock issued	252,972	7,500,000
Common stock price per share | $ / shares	$ 12	$ 12
Initial Public Offering [Member] | Common Stock [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares converted		8,577,571
Redeemable Convertible Preferred Stock [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Preferred stock outstanding					77,185,117	42,037,500	24,037,500
Redeemable Convertible Preferred Stock [Member] | Initial Public Offering [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Preferred stock outstanding		0

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016AUD
Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Research and development tax incentives	AUD 20,000,000
Tax incentive rate related to research and development	50.00%
Minimum [Member] | Australia [Member]
Summary Of Significant Accounting Policy [Line Items]
Tax incentive rate related to research and development	50.00%

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 85,169	$ 10,004
Total financial liabilities		2,123
Redeemable Convertible Preferred Stock Tranche Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities		1,643
Redeemable Convertible Preferred Stock Warrant Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities		480
Corporate Bonds Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	21,841	7,368
Governmental Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	41,289
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	11,270	2,136
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	10,769	500
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	11,270	2,136
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	11,270	2,136
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	73,899	7,868
Level 2 [Member] | Corporate Bonds Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	21,841	7,368
Level 2 [Member] | Governmental Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	41,289
Level 2 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 10,769	500
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities		2,123
Level 3 [Member] | Redeemable Convertible Preferred Stock Tranche Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities		1,643
Level 3 [Member] | Redeemable Convertible Preferred Stock Warrant Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities		$ 480	$ 1,023

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Changes in Fair Value of Company's Level 3 Financial Instruments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items]
Financial liabilities, beginning balance	$ 2,123
Change in fair value upon revaluation	(525)	$ 543	$ (872)
Change in fair value upon revaluation	(4,194)	(626)	(897)
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock	(1,005)
Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock	(5,837)
Financial liabilities, ending balance		2,123
Redeemable Convertible Preferred Stock Tranche Liability [Member]
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items]
Financial liabilities, beginning balance	1,643
Financial liabilities, ending balance		1,643
Redeemable Convertible Preferred Stock Warrant Liability [Member]
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items]
Financial liabilities, beginning balance	480
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock	(1,000)
Financial liabilities, ending balance		480
Level 3 [Member]
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items]
Financial liabilities, beginning balance	2,123
Financial liabilities, ending balance		2,123
Level 3 [Member] | Redeemable Convertible Preferred Stock Tranche Liability [Member]
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items]
Financial liabilities, beginning balance	1,643
Issuance of Series C redeemable convertible preferred stock tranche liability		1,017
Change in fair value upon revaluation	4,194	626
Settlement of redeemable convertible preferred stock tranche liability due to the issuance of Series C redeemable convertible preferred stock	(5,837)
Financial liabilities, ending balance		1,643
Level 3 [Member] | Redeemable Convertible Preferred Stock Warrant Liability [Member]
Fair Value Liabilities Measured On Recurring and Nonrecurring Basis [Line Items]
Financial liabilities, beginning balance	480	1,023
Change in fair value upon revaluation	525	(543)
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock	$ (1,005)
Financial liabilities, ending balance		$ 480	$ 1,023

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Cash Equivalents and Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Cash Equivalents and Available-for-Sale Securities [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	$ 85,241	$ 10,009
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	2
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(74)	(5)
Total cash equivalents and available-for-sale securities, Fair Value	85,169	10,004
Cash equivalents	18,504	2,136
Available-for-sale securities - current	56,515	7,868
Available-for-sale securities - noncurrent	10,150
Corporate Bonds Member]
Cash Equivalents and Available-for-Sale Securities [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	21,886	7,373
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(45)	(5)
Total cash equivalents and available-for-sale securities, Fair Value	21,841	7,368
Governmental Bonds [Member]
Cash Equivalents and Available-for-Sale Securities [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	41,316
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	2
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(29)
Total cash equivalents and available-for-sale securities, Fair Value	41,289
Money Market Funds [Member]
Cash Equivalents and Available-for-Sale Securities [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	11,270	2,136
Total cash equivalents and available-for-sale securities, Fair Value	11,270	2,136
Commercial Paper [Member]
Cash Equivalents and Available-for-Sale Securities [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	10,769	500
Total cash equivalents and available-for-sale securities, Fair Value	$ 10,769	$ 500

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Balance Sheet Components [Line Items]
Realized gains or losses on available-for-sale securities	$ 0	$ 0
Depreciation expense	317,000	247,000	$ 258,000
Property and equipment, net	562,000	609,000
Australia [Member]
Balance Sheet Components [Line Items]
Property and equipment, net	$ 8,000	$ 51,000
Maximum [Member]
Balance Sheet Components [Line Items]
Available-for-sale securities current contractual maturity	1 year	1 year
Available-for-sale securities - noncurrent	2 years
Minimum [Member]
Balance Sheet Components [Line Items]
Available-for-sale securities - noncurrent	1 year

Balance Sheet Components - Su42

Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid clinical and research related expenses	$ 2,488	$ 1,253
Other	906	305
Prepaid expenses and other current assets	$ 3,394	$ 1,558

Balance Sheet Components - Su43

Balance Sheet Components - Summary of Property and Equipment Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 1,875	$ 1,640
Less: accumulated depreciation and amortization	(1,313)	(1,031)
Property and equipment, net	562	609
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,650	1,452
Furniture and Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	163	140
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 62	$ 48

Balance Sheet Components - Su44

Balance Sheet Components - Summary of Accrued Expenses and Other Payables (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Accrued clinical and research related expenses	$ 3,617	$ 976
Accrued employee related expenses	1,420	754
Other	235	149
Total accrued expenses and other payables	$ 5,272	$ 1,879

Research Collaboration and Li45

Research Collaboration and License Agreement - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	$ 25,705,000	$ 11,831,000	$ 7,459,000
Research Collaboration and License Agreement [Member] | PTG-300 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment based on agreement	250,000
Potential milestone payment on collaboration arrangement	250,000
Research and development expense	250,000	$ 0	$ 0
Maximum [Member] | Research Collaboration and License Agreement [Member] | PTG-300 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate milestone payment	$ 128,500,000

Government Programs - Additiona

Government Programs - Additional Information (Detail)

1 Months Ended

3 Months Ended

12 Months Ended

Dec. 31, 2016USD ($)

Dec. 31, 2016AUD

Oct. 31, 2016USD ($)

Oct. 31, 2016AUD

Jul. 31, 2016USD ($)

Sep. 30, 2015USD ($)

Mar. 31, 2016USD ($)

Mar. 31, 2016AUD

Dec. 31, 2016USD ($)

Dec. 31, 2016AUD

Dec. 31, 2015USD ($)

Dec. 31, 2015AUD

Dec. 31, 2014USD ($)

Dec. 31, 2014AUD

Dec. 31, 2016AUD

Dec. 31, 2015AUD

Government Programs [Line Items]

Research and development tax incentive receivable

$ 2,241,000

$ 2,241,000

$ 715,000

Maximum [Member]

Government Programs [Line Items]

Research and development tax incentives | AUD

AUD 20,000,000

Tax incentive rate related to research and development

50.00%

50.00%

SBIR Grant [Member]

Government Programs [Line Items]

Reduction of research and development expenses related to tax

$ 169,000

155,000

Research and development grants

$ 219,000

$ 224,000

Grants receivable

$ 100,000

100,000

155,000

Australian Taxation Office [Member]

Government Programs [Line Items]

Research and development tax incentives

$ 2,200,000

AUD 3,000,000

Australian Taxation Office [Member] | Research and Development Tax Incentive Receivable [Member]

Government Programs [Line Items]

Research and development tax incentives

700,000

1,000,000

Australian Taxation Office [Member] | Maximum [Member]

Government Programs [Line Items]

Tax incentive rate related to research and development

50.00%

50.00%

Overseas Findings [Member] | Australian Taxation Office [Member]

Government Programs [Line Items]

Research and development tax incentive receivable

$ 2,200,000

2,200,000

715,000

AUD 3,100,000

AUD 978,000

Deferred tax incentive

$ 1,500,000

AUD 2,000,000

$ 182,000

AUD 237,000

Research and Development Tax Incentive [Member] | Australian Taxation Office [Member]

Government Programs [Line Items]

Reduction of research and development expenses related to tax

$ 1,600,000

AUD 2,200,000

$ 4,000,000

AUD 5,300,000

$ 736,000

AUD 978,000

$ 577,000

AUD 639,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Security deposit	$ 30,000
Lease expiration date	2018-04
Rent expense	$ 408,000	$ 280,000	$ 184,000

Commitments and Contingencies48

Commitments and Contingencies - Summary of Future Minimum Lease Payments (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Leases [Abstract]
2,017	$ 368
2,018	87
Total	$ 455

Preferred Stock Warrants - Addi

Preferred Stock Warrants - Additional Information (Detail)	1 Months Ended				12 Months Ended
	Jul. 31, 2016IPO	Apr. 30, 2016USD ($)shares	Aug. 31, 2014USD ($)shares	Aug. 31, 2013$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)	May 31, 2016shares	Mar. 31, 2016shares
Class of Warrant or Right [Line Items]
Redeemable convertible preferred stock, shares issued | shares					0	77,185,117
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants					$ 22,488,000	$ 17,362,000	$ 9,000,000
Remeasured fair value of warrants		$ 1,000,000
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock					1,005,000
Change in fair value of redeemable convertible preferred stock warrant liability					525,000	$ (543,000)	$ 872,000
Redeemable Convertible Preferred Stock Warrant Liability [Member]
Class of Warrant or Right [Line Items]
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock					$ 1,000,000
Option Pricing Model [Member]
Class of Warrant or Right [Line Items]
Percentage of weighted value per share		67.00%
PWERM [Member]
Class of Warrant or Right [Line Items]
Percentage of weighted value per share		33.00%
Fair value assumptions probabilities, number of IPO scenarios | IPO	3
First Tranche Warrants [Member]
Class of Warrant or Right [Line Items]
Number of convertible preferred stock issued upon exercise of stock warrants | shares				2,000,000
Probability of exercisability percentage						95.00%
Second Tranche Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants issued date					Aug. 15, 2014
Probability of exercisability percentage						0.00%
Preferred Stock Warrant Liability [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding, fair value						$ 480,000
Risk-free interest rate		0.73%				0.90%
Expected life		2 years				1 year 7 months 6 days
Expected volatility		52.00%				57.00%
Series B Redeemable Convertible Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Number of convertible preferred stock issued upon exercise of stock warrants | shares				4,000,000
Warrants exercise price | $ / shares				$ 0.01
Percentage of warrants exercisable upon new product announcement				50.00%
Risk-free interest rate			0.50%
Expected life			0 years
Probability of exercisability percentage			100.00%
Redeemable convertible preferred stock, shares issued | shares		1,999,998	18,000,000
Redeemable convertible preferred stock, warrants exercisable | shares									2,000,000
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants		$ 20,000	$ 9,000,000
Number of redeemable convertible preferred stock expired unexercised | shares								2,000,000

Redeemable Convertible Prefer50

Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Apr. 30, 2016	Aug. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Aug. 16, 2016
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued			0	77,185,117
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants			$ 22,488,000	$ 17,362,000	$ 9,000,000
Shares issued upon conversion of preferred stock						8,577,571
Redeemable convertible preferred stock, shares outstanding			0	77,185,117
Redeemable convertible preferred stock redemption date			2022-07
Redeemable convertible preferred stock, period accretion			$ 558,000	$ 75,000	$ 146,000
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued	1,999,998	18,000,000
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants	$ 20,000	$ 9,000,000

Redeemable Convertible Prefer51

Redeemable Convertible Preferred Stock - Summary of Redeemable Convertible Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2015	Aug. 31, 2014
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized	0	126,374,911
Convertible preferred stock, shares issued and outstanding		77,185,117
Convertible preferred stock, carrying value		$ 36,996
Convertible preferred stock, aggregate liquidation preference		$ 41,538
Series A Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Convertible preferred stock, original issue price		$ 1
Convertible preferred stock, shares authorized		6,037,500
Convertible preferred stock, shares issued and outstanding		6,037,500
Convertible preferred stock, carrying value		$ 1,751
Convertible preferred stock, aggregate liquidation preference		$ 6,038
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Convertible preferred stock, original issue price		$ 0.5000		$ 0.50
Convertible preferred stock, shares authorized		40,000,000
Convertible preferred stock, shares issued and outstanding		36,000,000
Convertible preferred stock, carrying value		$ 18,825
Convertible preferred stock, aggregate liquidation preference		$ 18,000
Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Convertible preferred stock, original issue price		$ 0.4979	$ 0.4979
Convertible preferred stock, shares authorized		80,337,411	80,337,411
Convertible preferred stock, shares issued and outstanding		35,147,617
Convertible preferred stock, carrying value		$ 16,420
Convertible preferred stock, aggregate liquidation preference		$ 17,500

Redeemable Convertible Prefer52

Redeemable Convertible Preferred Stock Tranche Liability - Additional Information (Detail) - USD ($)	Jul. 10, 2015	Apr. 30, 2016	Mar. 31, 2016	Aug. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 31, 2015
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Redeemable convertible preferred stock, shares issued					0	77,185,117
Redeemable convertible preferred stock, proceeds					$ 22,488,000	$ 17,362,000	$ 9,000,000
Fair value of redeemable convertible preferred stock liability reclassified			$ 5,800,000	$ 2,300,000	$ 5,837,000		2,308,000
Redeemable convertible preferred stock, authorized					0	126,374,911
Change in fair value of redeemable convertible preferred stock tranche liabilities					$ 4,194,000	$ 626,000	897,000
Second Tranche Warrants [Member]
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Probability of exercisability percentage						0.00%
Series C Redeemable Convertible Preferred Stock [Member]
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Redeemable convertible preferred stock, shares issued	35,147,617		45,189,794
Redeemable convertible preferred stock, proceeds	$ 17,500,000		$ 22,500,000
Fair value of redeemable convertible preferred stock liability	$ 1,000,000		$ 5,800,000			$ 1,600,000
Probability of exercisability percentage	90.00%					95.00%
Fair value assumptions, expected term	1 year		2 years			6 months 11 days
Fair value assumptions, risk-free interest rate	0.50%		0.73%			0.90%
Redeemable convertible preferred stock, price per share						$ 0.4979		$ 0.4979
Redeemable convertible preferred stock, authorized						80,337,411		80,337,411
Fair value assumptions, expected volatility			52.00%
Change in fair value of redeemable convertible preferred stock tranche liabilities					$ 4,200,000	$ 626,000	$ 897,000
Series C Redeemable Convertible Preferred Stock [Member] | Option Pricing Model [Member]
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Fair value assumptions, weighted volatility rate			67.00%
Series C Redeemable Convertible Preferred Stock [Member] | PWERM [Member]
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Fair value assumptions, weighted volatility rate			33.00%
Series C Redeemable Convertible Preferred Stock [Member] | Second Tranche Warrants [Member]
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Additional shares to be issued upon the achievement of certain development milestones	45,189,794
Series B Redeemable Convertible Preferred Stock [Member]
Redeemable Convertible Preferred Stock Tranche Liability [Line Items]
Redeemable convertible preferred stock, shares issued		1,999,998		18,000,000
Redeemable convertible preferred stock, proceeds		$ 20,000		$ 9,000,000
Fair value of redeemable convertible preferred stock liability				$ 2,300,000
Probability of exercisability percentage				100.00%
Fair value assumptions, expected term				0 years
Fair value assumptions, risk-free interest rate				0.50%
Redeemable convertible preferred stock, price per share				$ 0.50		$ 0.5000
Redeemable convertible preferred stock, authorized						40,000,000

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Stock Reserved for Issuance (Detail) - shares	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Total	2,558,157	6,579,361
Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Total		5,323,103
Options Issued and Outstanding [Member]
Class of Stock [Line Items]
Total	2,393,829	833,178
Redeemable Convertible Preferred Stock Warrant Liability [Member]
Class of Stock [Line Items]
Total		275,861
Options Available for Future Grants [Member]
Class of Stock [Line Items]
Total	164,328	147,219

Equity Plans - Additional Infor

Equity Plans - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		2,558,157	6,579,361
Aggregate intrinsic value of options exercised		$ 169,000
Options, weighted-average grant-date fair value		$ 8.20	$ 0.69	$ 0.82
Expected dividend yield		0.00%	0.00%	0.00%
Stock-based compensation expense		$ 2,130,000	$ 99,000	$ 42,000
Total unrecognized stock-based compensation costs related to stock options		$ 12,600,000
Period of unrecognized stock-based compensation costs to be recognized		3 years 1 month 13 days
2016 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional vesting years	3 years
Common stock reserved for issuance	1,200,000	1,200,000
Vesting percentage of requisite service period	25.00%
2016 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Exercise price as a percentage of the fair market value of common stock on grant date	100.00%
2016 Equity Incentive Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as a percentage of the fair market value for option holding more than 10% total combined voting power	110.00%
Minimum percentage of voting right to grant stock option	10.00%
2016 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	150,000
Expected dividend yield		0.00%
Percentage of discount from fair market value of common stock on offering date	85.00%
Maximum percentage of outstanding stock issuance	1.00%
Maximum number of outstanding stock issuance	300,000
Maximum period for additional outstanding stock issuance	10 years
2016 Employee Stock Purchase Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of payroll deductions on eligible compensation	15.00%
2007 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		10 years
Additional vesting years		4 years
Cliff vesting period		1 year
Non-employee Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted		59,647	4,816	11,805
Stock-based compensation expense		$ 505,000	$ 15,000	$ 5,000

Equity Plans - Schedule of Acti

Equity Plans - Schedule of Activity under Equity Incentive Plans (Detail) - 2007 and 2016 Equity Incentive Plans [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Available for Grant, Beginning balance	147,219	116,832	70,082
Options Available for Grant, Additional options authorized	1,697,088	431,411	240,425
Options Available for Grant, Options granted	(1,679,979)	(408,623)	(199,519)
Options Available for Grant, Options exercised	0	0	0
Options Available for Grant, Options forfeited		7,599	5,844
Options Available for Grant, Ending balance	164,328	147,219	116,832	70,082
Number of Options Outstanding, Beginning balance	833,178	476,006	284,879
Number of Options Outstanding, Options granted	1,679,979	408,623	199,519
Number of Options Outstanding, Options exercised	(119,328)	(43,852)	(2,548)
Number of Options Outstanding, Options forfeited		(7,599)	(5,844)
Number of Options Outstanding, Ending balance	2,393,829	833,178	476,006	284,879
Weighted-Average Exercise Price Per Share, Beginning balance	$ 1.33	$ 1.40	$ 1.10
Number of Options Outstanding, Options exercisable	492,714
Weighted-Average Exercise Price Per Share, Options granted	$ 14.24	1.24	1.83
Number of Options Outstanding, Options vested and expected to vest	2,369,135
Weighted-Average Exercise Price Per Share, Options exercised	$ 1.28	1.30	1.30
Weighted-Average Exercise Price Per Share, Options forfeited		1.40	1.13
Weighted-Average Exercise Price Per Share, Ending balance	10.39	$ 1.33	$ 1.40	$ 1.10
Weighted-Average Exercise Price Per Share, Options exercisable	5.19
Weighted-Average Exercise Price Per Share, Options vested and expected to vest	$ 10.37
Weighted-Average Remaining Contractual Life (years)	8 years 9 months 15 days	8 years 6 months 22 days	8 years 15 days	7 years 11 months 1 day
Weighted-Average Remaining Contractual Life (years), Options exercisable	7 years 8 months 12 days
Weighted-Average Remaining Contractual Life (years), Options vested and expected to vest	8 years 9 months 15 days
Aggregate Intrinsic Value, Options Outstanding	$ 27,820
Aggregate Intrinsic Value, Options exercisable	8,286
Aggregate Intrinsic Value, Options vested and expected to vest	$ 27,596

Equity Plans - Schedule of Gran

Equity Plans - Schedule of Grant-date Fair Value of Employee and Director Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		5 years 10 months 21 days	6 years 29 days
Expected volatility		59.80%	64.70%
Expected volatility, Minimum	62.50%
Expected volatility, Maximum	64.80%
Risk-free interest rate			1.89%
Risk-free interest rate, Minimum	1.27%	1.57%
Risk-free interest rate, Maximum	1.79%	1.58%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 1 month 28 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 11 months 12 days

Equity Plans - Schedule of Gr57

Equity Plans - Schedule of Grant-date Fair Value of Non-employees Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		5 years 10 months 21 days	6 years 29 days
Expected volatility		59.80%	64.70%
Expected volatility, Minimum	62.50%
Expected volatility, Maximum	64.80%
Risk-free interest rate			1.89%
Risk-free interest rate, Minimum	1.27%	1.57%
Risk-free interest rate, Maximum	1.79%	1.58%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 1 month 28 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 11 months 12 days
Non-employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		6 years 9 months 18 days	9 years 4 months 24 days
Expected volatility		59.80%	64.70%
Expected volatility, Minimum	62.50%
Expected volatility, Maximum	62.80%
Risk-free interest rate		1.95%	2.34%
Risk-free interest rate, Minimum	1.29%
Risk-free interest rate, Maximum	1.79%
Dividend yield	0.00%	0.00%	0.00%
Non-employees [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 7 months 2 days
Non-employees [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	9 years 11 months 19 days

Equity Plans - Schedule of Fair

Equity Plans - Schedule of Fair Value of Rights under 2016 ESPP Using Black-Scholes Option Pricing Model Assumptions (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		5 years 10 months 21 days	6 years 29 days
Expected volatility		59.80%	64.70%
Risk-free interest rate			1.89%
Dividend yield	0.00%	0.00%	0.00%
2016 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	7 months 6 days
Expected volatility	52.48%
Risk-free interest rate	0.45%
Dividend yield	0.00%

Equity Plans - Schedule of Stoc

Equity Plans - Schedule of Stock-based Compensation Expense for Employees and Non-employees for Stock Options and the 2016 ESPP (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,130	$ 99	$ 42
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,080	39	17
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,050	$ 60	$ 25

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Provision for income taxes	$ 0	$ 0	$ 0
Increase in valuation allowance	13,400,000	$ 3,000,000	$ 2,900,000
Research and development tax credit carryforwards, state	600,000
Research and development tax credit carryforwards, federal	$ 1,100,000
Federal research and development tax credits, expiration start date	2,035
Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
Open tax year	2,012
Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
Open tax year	2,016
Australian Taxation Office [Member]
Income Tax Disclosure [Line Items]
Accumulated tax losses carry forward	$ 9,200,000
Domestic Tax Authority [Member]
Income Tax Disclosure [Line Items]
Accumulated tax losses carry forward	$ 48,000,000
Net operating loss carryforwards expiration year	2,033
State and Local Jurisdiction [Member]
Income Tax Disclosure [Line Items]
Accumulated tax losses carry forward	$ 37,700,000
Net operating loss carryforwards expiration year	2,033

Income Taxes - Domestic and For

Income Taxes - Domestic and Foreign Components of Net Loss (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Domestic									$ (34,977)	$ (10,483)	$ (9,515)
Foreign									(2,200)	(4,375)	(1,557)
Total net loss	$ (11,248)	$ (7,084)	$ (7,098)	$ (11,747)	$ (5,493)	$ (3,449)	$ (3,219)	$ (2,697)	$ (37,177)	$ (14,858)	$ (11,072)

Income Taxes - Summary of Effec

Income Taxes - Summary of Effective Tax Rate of Provision For Income Taxes Differs From Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	34.00%	34.00%	34.00%
State taxes, net of federal benefit	6.50%	(2.70%)	4.10%
Warrant revaluation	(4.30%)	(0.20%)	(5.50%)
Foreign tax rate difference	(1.60%)	(11.80%)	(6.80%)
Change in valuation allowance	(36.00%)	(19.90%)	(26.50%)
Other	1.40%	0.60%	0.70%
Provision for income taxes	0.00%	0.00%	0.00%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 21,501	$ 9,513
Depreciation and amortization	419	480
Accruals/other	908	293
Research and development credits & foreign credits	1,143	285
Total deferred tax assets	23,971	10,571
Valuation allowance	(23,971)	(10,571)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 805
Additions based on tax positions related to in prior years	707	$ 690
Additions based on tax positions related to current year	619	115
Balance at end of year	$ 2,131	$ 805

Net Loss per Share Attributab65

Net Loss per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss	$ (11,248)	$ (7,084)	$ (7,098)	$ (11,747)	$ (5,493)	$ (3,449)	$ (3,219)	$ (2,697)	$ (37,177)	$ (14,858)	$ (11,072)
Accretion of redeemable convertible preferred stock									(558)	(75)	(146)
Net loss attributable to common stockholders									$ (37,735)	$ (14,933)	$ (11,218)
Denominator:
Weighted-average shares used to compute net loss per common share, basic and diluted									6,501,796	251,717	227,197
Net loss per share attributable to common stockholders, basic and diluted	$ (0.67)	$ (0.87)	$ (19.07)	$ (40.96)	$ (20.31)	$ (12.79)	$ (13.78)	$ (11.75)	$ (5.80)	$ (59.32)	$ (49.38)

Net Loss per Share Attributab66

Net Loss per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share	2,393,829	6,432,142	3,651,001
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share		5,323,103	2,899,134
Warrants to Purchase Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share		275,861	275,861
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share	2,393,829	833,178	476,006

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Mar. 31, 2017
Subsequent Event [Line Items]
Lease commencement date	Jul. 1, 2017
Lease expiration date	Jun. 30, 2024
Aggregate minimum lease payments	$ 455,000
Security deposit	$ 30,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Aggregate minimum lease payments		$ 13,400,000
Security deposit		$ 450,000

Supplementary Financial Data 68

Supplementary Financial Data (Unaudited) - Summary of Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Loss from operations	$ (11,397)	$ (7,138)	$ (7,091)	$ (7,040)	$ (5,001)	$ (4,021)	$ (3,083)	$ (2,689)	$ (32,666)	$ (14,794)	$ (9,319)
Net loss	$ (11,248)	$ (7,084)	$ (7,098)	$ (11,747)	$ (5,493)	$ (3,449)	$ (3,219)	$ (2,697)	$ (37,177)	$ (14,858)	$ (11,072)
Net loss per share of common stock attributable to common stockholders, basic and diluted	$ (0.67)	$ (0.87)	$ (19.07)	$ (40.96)	$ (20.31)	$ (12.79)	$ (13.78)	$ (11.75)	$ (5.80)	$ (59.32)	$ (49.38)