Protagonist Therapeutics (PTGX) 10-Q 8 Aug 17 2017 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Jul. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Trading Symbol	PTGX
Entity Registrant Name	PROTAGONIST THERAPEUTICS, INC
Entity Central Index Key	1,377,121
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		16,902,761

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 10,365	$ 21,084
Restricted cash - current	10	10
Available-for-sale securities - current	54,127	56,515
Research and development tax incentive receivable	2,881	2,241
Prepaid expenses and other current assets	1,743	3,394
Total current assets	69,126	83,244
Property and equipment, net	903	562
Restricted cash - noncurrent	450	0
Available-for-sale securities - noncurrent	0	10,150
Other assets	0	34
Total assets	70,479	93,990
Current liabilities:
Accounts payable	2,639	1,163
Accrued expenses and other payables	6,727	5,272
Total current liabilities	9,366	6,435
Deferred rent	83	0
Total liabilities	9,449	6,435
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.00001 par value, 10,000,000 shares authorized; and no shares issued and outstanding as of June 30, 2017 and December 31, 2016	0	0
Common stock, $0.00001 par value, 90,000,000 shares authorized; 16,899,261 and 16,722,280 shares issued and outstanding as of June 30, 2017 and December 31, 2016, respectively	0	0
Additional paid-in capital	154,700	152,393
Accumulated other comprehensive gain (loss)	3	(245)
Accumulated deficit	(93,673)	(64,593)
Total stockholders’ equity	61,030	87,555
Total liabilities and stockholders’ equity	$ 70,479	$ 93,990

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	10,000,000
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	90,000,000
Common stock, shares issued	16,899,261	16,722,280
Common stock, shares outstanding	16,899,261	16,722,280

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating expenses:
Research and development	$ 12,007	$ 5,696	$ 23,289	$ 11,321
General and administrative	3,124	1,395	6,115	2,810
Total operating expenses	15,131	7,091	29,404	14,131
Loss from operations	(15,131)	(7,091)	(29,404)	(14,131)
Interest income	152	27	324	39
Change in fair value of redeemable convertible preferred stock tranche and warrant liabilities	0	0	0	(4,719)
Other expense	0	(34)	0	(34)
Net loss	(14,979)	(7,098)	(29,080)	(18,845)
Net loss attributable to common stockholders	$ (14,979)	$ (7,323)	$ (29,080)	$ (19,110)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.89)	$ (19.07)	$ (1.73)	$ (56.90)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	16,875,627	383,910	16,821,225	335,855

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (14,979)	$ (7,098)	$ (29,080)	$ (18,845)
Other comprehensive loss:
Gain (loss) on translation of foreign operations	14	(4)	251	(2)
Unrecognized gain (loss) on available-for-sale securities	11	(1)	(3)	4
Comprehensive loss	$ (14,954)	$ (7,103)	$ (28,832)	$ (18,843)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (29,080)	$ (18,845)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	181	159
(Gain) loss on disposal of property and equipment	(65)	34
Amortization of premium on available-for-sale securities	272	72
Stock-based compensation	1,845	162
Change in fair value associated with redeemable convertible preferred stock tranche liability	0	4,194
Change in fair value of redeemable convertible preferred stock warrant liability	0	525
Changes in operating assets and liabilities:
Research and development tax incentive receivable	(479)	(1,030)
Prepaid expenses and other current assets	1,698	1,134
Other assets	0	(4)
Accounts payable	1,428	85
Accrued expenses and other payables	1,517	202
Net cash used in operating activities	(22,683)	(13,312)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of property and equipment	(420)	(279)
Purchase of available-for-sale securities	(8,002)	(6,396)
Proceeds from maturities of available-for-sale securities	20,265	7,788
Net cash provided by investing activities	11,843	1,113
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	0	22,508
Proceeds from issuance of common stock upon exercise of stock options and purchases under employee stock purchase plan	461	143
Payment of deferred offering costs	0	(770)
Net cash provided by financing activities	461	21,881
Effect of exchange rate changes on cash, cash equivalents and restricted cash	110	31
Net (decrease) increase in cash, cash equivalents and restricted cash	(10,269)	9,713
Cash, cash equivalents and restricted cash, beginning of period	21,094	4,065
Cash, cash equivalents and restricted cash, end of period	10,365	13,768
SUPPLEMENTAL DISCLOSURES OF NON-CASH FINANCING AND INVESTING INFORMATION
Settlement of fair value of redeemable convertible preferred stock liability	0	5,837
Accretion of redeemable convertible preferred stock	0	265
Deferred offering costs in accounts payable and accrued liabilities	0	696
Acquisition of equipment in trade-in	185	0
Purchase of property and equipment in accounts payable and accrued liabilities	42	0
Reclassification of preferred stock warrant liability to equity	$ 0	$ 1,005

Organization and Description of

Organization and Description of Business	6 Months Ended
	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	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 Newark, California. The Company is a clinical-stage biopharmaceutical company with a proprietary technology platform which is utilized to discover and develop novel peptide-based drugs to address significant unmet medical needs. Protagonist Pty Limited (“Protagonist Australia”) is a wholly-owned subsidiary of the Company and is located in Brisbane, Australia. Protagonist Australia was incorporated in Australia in September 2001. The Company became the parent of Protagonist Australia pursuant to a transaction in which all of the issued and outstanding capital stock of Protagonist Australia was exchanged for shares of the Company’s common stock and Series A preferred stock. The Company manages its operations as a single operating segment. Liquidity The Company has incurred net losses from operations since inception and has an accumulated deficit of $93.7 million as of June 30, 2017 . 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 will also continue to seek funds through equity or debt financings, collaborative or other arrangements with corporate sources, or through other sources of financing, but there is no assurance that such financing will be available at terms acceptable to the Company, if at all. Initial Public Offering On August 10, 2016, the Company’s registration statement on Form S-1 (File Nos. 333-212476 and 333-213071) related 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. There were no shares of redeemable convertible preferred stock outstanding at June 30, 2017 or December 31, 2016 . In September 2016, the Company issued an additional 252,972 shares of its 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, after deducting offering costs paid by the Company. 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 stock split. All issued and outstanding common stock, options to purchase common stock and per share amounts contained in the condensed consolidated financial statements have been retroactively adjusted to reflect the reverse stock split for all periods presented.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted, and accordingly the consolidated balance sheet as of December 31, 2016 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete consolidated financial statements. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three and six months ended June 30, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017 or for any other interim period or for any other future year. The accompanying interim unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2016 included in the Company’s Annual Report on Form 10-K, filed with the SEC on March 7, 2017. Principles of Consolidation The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany transactions and balances have been eliminated upon consolidation. Use of Estimates The preparation of the condensed consolidated financial statements in conformity with 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 condensed 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, 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 of the Company’s cash is held by two financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The primary focus of the Company’s investment strategy is to preserve capital and to meet liquidity requirements. The Company’s cash equivalents and available-for-sale securities are managed by external managers within the guidelines of the Company’s investment policy. The Company’s investment policy addresses the level of credit exposure by limiting concentration in any one corporate issuer and establishing a minimum allowable credit rating. To manage its credit risk exposure, the Company maintains its portfolio of cash equivalents and available-for-sale securities in fixed income securities denominated and payable in U.S. dollars. Permissible investments of fixed income securities include obligations of the U.S. government and its agencies, money market instruments including commercial paper and negotiable certificates of deposit, and highly rated corporate debt obligations and money market funds. The Company has not experienced any material credit losses on its investments. 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. Restricted Cash Restricted cash consists of cash balances primarily held as security in connection with the Company’s corporate credit card and a letter of credit related to the Company's facility lease entered into in March 2017. Cash as Reported in Consolidated Statements of Cash Flows Cash as reported in the unaudited condensed consolidated statements of cash flows includes the aggregate amounts of cash and cash equivalents and the restricted cash as presented on the consolidated balance sheets. Cash as reported in the unaudited condensed consolidated statements of cash flows consists of (in thousands): June 30, 2017 2016 Cash and cash equivalents $ 10,365 $ 13,768 Restricted cash - current 10 10 Restricted cash - noncurrent 450 — Cash balance in condensed consolidated statements of cash flows $ 10,825 $ 13,778 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 greater than three months but no longer than 365 days as of the balance sheet date. Long-term marketable securities have maturities of 365 days or longer 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 to all financial assets and liabilities that are recognized or disclosed at fair value in the condensed 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 approximates fair value due to their short-term maturities. See Note 4, Fair Value Measurements, regarding the fair value of the Company’s other financial assets and liabilities. 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 pre-clinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated services provided but not yet invoiced, and includes these costs in accrued expenses and other payables in the condensed consolidated balance sheets and within research and development expense in the condensed 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 at each balance sheet date. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued liabilities and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled, and the rate of patient enrollment 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. Research and Development Costs Research and development costs are expensed as incurred, unless there is an alternate future use in other research and development projects or otherwise. Research and development costs include salaries and benefits, stock-based compensation expense, laboratory supplies and facility-related overhead, outside contracted services including clinical trial costs, manufacturing and process development costs for both clinical and preclinical materials, research costs, development milestone payments under license and collaboration agreements, and other consulting services. 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. 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 annual turnover of less than AUD 20.0 million and cannot be controlled by income tax exempt entities. The research and development tax incentive is recognized as a reduction to 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% of 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 expense 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 to reflect that the funds are owed to the Company for the period the eligible costs are incurred. 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, if applicable. 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. Recently Adopted Accounting Pronouncements In November 2015, Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes , which is intended to simplify and improve how deferred income taxes are classified on the balance sheet. This guidance eliminates the current requirement to present deferred tax assets and liabilities as current and noncurrent in a classified balance sheet and now requires entities to classify all deferred tax assets and liabilities as noncurrent. The guidance is effective for annual periods beginning after December 15, 2016 and for interim periods within those annual periods, and early adoption is permitted. The Company adopted this guidance effective January 1, 2017. The adoption of this guidance did not have a material impact on the Company's financial position, results of operations or liquidity. In March 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, which is intended to simplify several aspects of accounting for employee share-based payment transactions, including 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 guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2016, and early adoption is permitted. The Company adopted this guidance effective January 1, 2017 and has elected to recognize forfeitures of share-based payment awards as they occur on a prospective basis. The impact of the adoption of ASU 2016-09 was not material to the Company’s condensed consolidated financial statements. The adoption of this guidance did not have a material impact on the income tax effects of share-based payment awards as the resulting change in the Company's deferred income tax assets is fully offset by a corresponding deferred income tax asset valuation allowance. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash , which requires the presentation of changes in restricted cash or restricted cash equivalents on the statement of cash flows. This guidance is effective for the fiscal years and interim periods within those years beginning after December 15, 2017, with early adoption permitted. The Company early adopted this guidance effective March 31, 2017, and, accordingly, amounts generally described as restricted cash are included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts of cash reflected on the accompanying consolidated statements of cash flows. The Company has adopted ASU 2016-18 retrospectively and has revised the prior period cash flows from investing activities, beginning cash balance, and ending cash balance to reflect the change in presentation of restricted cash. Other than the change in presentation in the accompanying consolidated statements of cash flows, the adoption of this guidance had no effect on the Company’s financial position, results of operations or liquidity. Recently Issued Accounting Pronouncements Not Adopted as of June 30, 2017 In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which amends the guidance for accounting for revenue from contracts with customers. In 2015 and 2016, the FASB issued additional ASUs that delayed the effective date and clarified various aspects of the new guidance, including principal vs. agent considerations, identifying performance obligations and licensing, and also included other improvements and practical expedients. The new standard will become effective for the Company on January 1, 2018, and early application is permitted for periods beginning on or after January 1, 2017. The new guidance applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under the new guidance, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of the new guidance, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company expects to modify its accounting policies to reflect the requirements of this guidance and expects to select the full retrospective transition method. The Company did not recognize revenue for the six months ended June 30, 2017 and 2016 and therefore, the planned adoption of this guidance will not affect the Company's consolidated financial statements and disclosures for these periods or future periods until the Company reports revenues. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) . Under the new guidance, (with the exception of short-term leases) at the commencement date, lessees will be required to recognize a lease liability and a right-of-use asset. Lessor accounting is largely unchanged, while lessees will no longer be provided with a source of off-balance sheet financing. This guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. Lessees (for capital and operating leases) are required to apply the modified retrospective transition method for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective method does not require any transition accounting for leases that did not exist before the earliest comparative period presented. While the Company continues to evaluate the impact of this guidance on its consolidated financial statements, it expects that its non-cancellable operating lease commitments will be subject to the new guidance and recognized as right-of-use assets and operating lease liabilities on the Company’s consolidated balance sheets, and that the adoption of this new guidance will not have a material impact on its results of operations or liquidity. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326) , which is intended to provide financial statement users with more useful information about expected credit losses on financial assets held by a reporting entity at each reporting date. The new standard replaces the existing incurred loss impairment methodology with a methodology that requires consideration of a broader range of reasonable and supportable forward-looking information to estimate all expected credit losses. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2019 and early adoption is permitted for fiscal years and interim periods within those years beginning after December 15, 2018. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , which clarifies the classification of certain cash receipts and cash payments in the statements of cash flow to eliminate the diversity in practice related to eight specific cash flow issues. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, and early adoption is permitted. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting, which provides guidance on the types of changes to the terms and conditions of share-based payment awards to which an entity would be required to apply modification accounting. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, and early adoption is permitted. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures.

Janssen Collaboration Agreement

Janssen Collaboration Agreement	6 Months Ended
	Jun. 30, 2017
Text Block [Abstract]
Janssen Collaboration Agreement	Janssen Collaboration Agreement Janssen Collaboration Agreement On May 26, 2017, the Company and Janssen Biotech, Inc., ("Janssen") entered into an exclusive license and collaboration agreement (the "Janssen Collaboration Agreement") for the development, manufacture and commercialization of PTG-200 worldwide for the treatment of Crohn's disease ("CD") and ulcerative colitis ("UC"). PTG-200 is the Company’s oral Interleukin 23 receptor ("IL-23R") antagonist drug candidate currently in pre-clinical development. The Janssen Collaboration Agreement became effective on July 13, 2017. Upon the effectiveness of the agreement, the Company became eligible for a non-refundable, upfront cash payment of $50.0 million from Janssen, which the Company expects to receive during the third quarter of 2017. Under the Janssen Collaboration Agreement, the Company granted to Janssen an exclusive worldwide license to develop, manufacture and commercialize PTG-200 and related IL-23R compounds for all indications, including CD and UC. The Company is responsible, at its own expense, for the conduct of the Phase 1 clinical trial for PTG-200, and Janssen will be responsible for the conduct of a potential Phase 2 clinical trial for PTG-200 in CD. All such clinical trials would be conducted in accordance with a mutually agreed upon clinical development plan and budget. Development costs for the Phase 2 clinical trial would be shared between the parties on an 80% / 20% basis, with Janssen assuming the larger share. Should Janssen elect to retain its license following completion of the Phase 2 clinical trial, it would be responsible, at its own expense, for the manufacture, continued development of, seeking regulatory approval for, and commercialization of PTG-200 worldwide. The parties’ development activities under the Janssen Collaboration Agreement through the Phase 2 clinical trial will be overseen by a joint governance structure which will have equal representation by both parties. Following the conclusion of the planned Phase 2A portion of the Phase 2 clinical trial, if Janssen elects to maintain its license rights and continue the development of PTG-200 in the Phase 2B portion of such clinical trial (the “First Opt-in Election”), the Company would be eligible to receive a $125 million payment. Following the conclusion of the planned Phase 2B portion of the Phase 2 clinical trial, if Janssen elects again to maintain its license rights (the “Second Opt-in Election”), the Company would be eligible to receive a $200 million payment. In addition to the opt-in fees, the Company is eligible to receive potential development, regulatory and sales milestone payments of up to an aggregate of $615 million and tiered royalties paid as a percentage of Janssen’s worldwide net sales at rates ranging from ten to the mid-teens, with certain customary reductions under certain circumstances. If Janssen does not make either the First Opt-in Election or the Second Opt-in Election, the Janssen Collaboration Agreement would terminate. If Janssen does not make the Second Opt-in Election, or if at any time after the Second Opt-in Election, Janssen terminates the Janssen Collaboration Agreement, the Company would be obligated to pay Janssen a royalty on worldwide net sales of PTG-200. The Company would also have an option to provide up to 30% of the required U.S. details for PTG-200 to prescribers, using its own sales force personnel, upon commercial launch in the United States. If such right is exercised by the Company, the Company’s detailing costs would be reimbursed by Janssen. The Janssen Collaboration Agreement contains customary representations, warranties and covenants by the Company and Janssen and includes an obligation by the Company not to develop or commercialize other compounds which also target IL-23R outside of the Janssen Collaboration Agreement until completion of the Phase 2B portion of the Phase 2 clinical trial. Each of the Company and Janssen is required to indemnify the other party against all losses and expenses related to breaches of its representations, warranties and covenants under the Janssen Collaboration Agreement. The Janssen Collaboration Agreement remains in effect until the royalty obligations cease following patent and regulatory expiry, unless terminated earlier. Either the Company or Janssen may terminate the Janssen Collaboration Agreement for uncured material breach. Janssen retains the right to terminate the Janssen Collaboration Agreement for convenience and without cause on written notice of a certain period to the Company. Upon a termination of the Janssen Collaboration Agreement, all rights revert back to the Company, and in certain circumstances, if such termination occurs during ongoing clinical trials, Janssen would, if requested, provide certain financial and operational support to the Company for the completion of such trials. 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 candidate. 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 acquired by the Company. The nomination of PTG-300 as a development candidate triggered a $250,000 payment from the Company to the former collaboration partner, which the Company recorded as a research and development expense during the three months ended March 31, 2016. The initiation of a Phase 1 clinical study for PTG-300 during the second quarter of 2017 triggered an additional $250,000 payment obligation from the Company to the former collaboration partner, which the Company recorded as a research and development expense during the three months ended June 30, 2017. The Company has the right, but not the obligation, to further develop and commercialize the product and, if the Company successfully develops and commercializes PTG-300 without a partner, the Company will pay the former collaboration partner up to an additional aggregate of $28.5 million for the achievement of certain development and regulatory milestone events and up to an additional aggregate of $100.0 million for the achievement of certain sales milestone events. In addition, the Company will pay the former collaboration partner a low single digit royalty on worldwide net sales of the product until the later of 10 years from the first commercial sale of the product or the expiration of the last patent covering the product.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	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 —Inputs are unadjusted quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2— Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3 —Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. In determining fair value, the Company utilizes quoted market prices, broker or dealer quotations, or valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible and 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 (in thousands). June 30, 2017 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 9,236 $ — $ — $ 9,236 Corporate bonds — 15,821 — 15,821 Commercial paper — 1,200 — 1,200 Government bonds — 37,106 — 37,106 Total financial assets $ 9,236 $ 54,127 $ — $ 63,363 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 Government bonds — 41,289 — 41,289 Total financial assets $ 11,270 $ 73,899 $ — $ 85,169 The Company's 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.

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Balance Sheet Components Cash Equivalents and Available-for-sale Securities Cash equivalents and available-for-sale securities consisted of the following (in thousands): June 30, 2017 Amortized Cost Gross Unrealized Gains Losses Fair Value Money market funds $ 9,236 $ — $ — $ 9,236 Corporate bonds 15,839 — (18 ) 15,821 Commercial paper 1,200 — — 1,200 Government bonds 37,163 — (57 ) 37,106 Total cash equivalents and available-for-sale securities $ 63,438 $ — $ (75 ) $ 63,363 Classified as: Cash equivalents $ 9,236 Available-for-sale securities - current 54,127 Available-for-sale securities - noncurrent — Total cash equivalents and available-for-sale securities $ 63,363 December 31, 2016 Amortized Cost Gross Unrealized 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 All available-for-sale securities - current held as of June 30, 2017 and December 31, 2016 had contractual maturities of less than one year. All available-for-sale securities - noncurrent held as of December 31, 2016 had contractual maturities of at least one year but less than two years. There were no available-for-sale securities - noncurrent held as of June 30, 2017 . There have been no material realized gains or losses on available-for-sale securities for the periods presented. Accrued Expenses and Other Payables Accrued expenses and other payables consisted of the following (in thousands): June 30, 2017 December 31, 2016 Accrued clinical and research related expenses $ 4,299 $ 3,617 Accrued employee related expenses 1,338 1,420 Accrued professional service fees 669 115 Accrued milestone payment to former collaboration partner 250 — Other 171 120 Total accrued expenses and other payables $ 6,727 $ 5,272

Research Collaboration and Lice

Research Collaboration and License Agreement	6 Months Ended
	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Research Collaboration and License Agreement	Janssen Collaboration Agreement Janssen Collaboration Agreement On May 26, 2017, the Company and Janssen Biotech, Inc., ("Janssen") entered into an exclusive license and collaboration agreement (the "Janssen Collaboration Agreement") for the development, manufacture and commercialization of PTG-200 worldwide for the treatment of Crohn's disease ("CD") and ulcerative colitis ("UC"). PTG-200 is the Company’s oral Interleukin 23 receptor ("IL-23R") antagonist drug candidate currently in pre-clinical development. The Janssen Collaboration Agreement became effective on July 13, 2017. Upon the effectiveness of the agreement, the Company became eligible for a non-refundable, upfront cash payment of $50.0 million from Janssen, which the Company expects to receive during the third quarter of 2017. Under the Janssen Collaboration Agreement, the Company granted to Janssen an exclusive worldwide license to develop, manufacture and commercialize PTG-200 and related IL-23R compounds for all indications, including CD and UC. The Company is responsible, at its own expense, for the conduct of the Phase 1 clinical trial for PTG-200, and Janssen will be responsible for the conduct of a potential Phase 2 clinical trial for PTG-200 in CD. All such clinical trials would be conducted in accordance with a mutually agreed upon clinical development plan and budget. Development costs for the Phase 2 clinical trial would be shared between the parties on an 80% / 20% basis, with Janssen assuming the larger share. Should Janssen elect to retain its license following completion of the Phase 2 clinical trial, it would be responsible, at its own expense, for the manufacture, continued development of, seeking regulatory approval for, and commercialization of PTG-200 worldwide. The parties’ development activities under the Janssen Collaboration Agreement through the Phase 2 clinical trial will be overseen by a joint governance structure which will have equal representation by both parties. Following the conclusion of the planned Phase 2A portion of the Phase 2 clinical trial, if Janssen elects to maintain its license rights and continue the development of PTG-200 in the Phase 2B portion of such clinical trial (the “First Opt-in Election”), the Company would be eligible to receive a $125 million payment. Following the conclusion of the planned Phase 2B portion of the Phase 2 clinical trial, if Janssen elects again to maintain its license rights (the “Second Opt-in Election”), the Company would be eligible to receive a $200 million payment. In addition to the opt-in fees, the Company is eligible to receive potential development, regulatory and sales milestone payments of up to an aggregate of $615 million and tiered royalties paid as a percentage of Janssen’s worldwide net sales at rates ranging from ten to the mid-teens, with certain customary reductions under certain circumstances. If Janssen does not make either the First Opt-in Election or the Second Opt-in Election, the Janssen Collaboration Agreement would terminate. If Janssen does not make the Second Opt-in Election, or if at any time after the Second Opt-in Election, Janssen terminates the Janssen Collaboration Agreement, the Company would be obligated to pay Janssen a royalty on worldwide net sales of PTG-200. The Company would also have an option to provide up to 30% of the required U.S. details for PTG-200 to prescribers, using its own sales force personnel, upon commercial launch in the United States. If such right is exercised by the Company, the Company’s detailing costs would be reimbursed by Janssen. The Janssen Collaboration Agreement contains customary representations, warranties and covenants by the Company and Janssen and includes an obligation by the Company not to develop or commercialize other compounds which also target IL-23R outside of the Janssen Collaboration Agreement until completion of the Phase 2B portion of the Phase 2 clinical trial. Each of the Company and Janssen is required to indemnify the other party against all losses and expenses related to breaches of its representations, warranties and covenants under the Janssen Collaboration Agreement. The Janssen Collaboration Agreement remains in effect until the royalty obligations cease following patent and regulatory expiry, unless terminated earlier. Either the Company or Janssen may terminate the Janssen Collaboration Agreement for uncured material breach. Janssen retains the right to terminate the Janssen Collaboration Agreement for convenience and without cause on written notice of a certain period to the Company. Upon a termination of the Janssen Collaboration Agreement, all rights revert back to the Company, and in certain circumstances, if such termination occurs during ongoing clinical trials, Janssen would, if requested, provide certain financial and operational support to the Company for the completion of such trials. 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 candidate. 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 acquired by the Company. The nomination of PTG-300 as a development candidate triggered a $250,000 payment from the Company to the former collaboration partner, which the Company recorded as a research and development expense during the three months ended March 31, 2016. The initiation of a Phase 1 clinical study for PTG-300 during the second quarter of 2017 triggered an additional $250,000 payment obligation from the Company to the former collaboration partner, which the Company recorded as a research and development expense during the three months ended June 30, 2017. The Company has the right, but not the obligation, to further develop and commercialize the product and, if the Company successfully develops and commercializes PTG-300 without a partner, the Company will pay the former collaboration partner up to an additional aggregate of $28.5 million for the achievement of certain development and regulatory milestone events and up to an additional aggregate of $100.0 million for the achievement of certain sales milestone events. In addition, the Company will pay the former collaboration partner a low single digit royalty on worldwide net sales of the product until the later of 10 years from the first commercial sale of the product or the expiration of the last patent covering the product.

Government Programs

Government Programs	6 Months Ended
	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Government Programs	Government Programs Research and Development Tax Incentive The Company recognized AUD 501,000 ( $377,000 ) and AUD 635,000 ( $480,000 ) as a reduction of research and development expenses for the three and six months ended June 30, 2017, respectively, in connection with the research and development tax incentive from Australia. The Company recognized AUD 666,000 ( $498,000 ) and AUD 1.4 million ( $1.0 million ) as a reduction of research and development expenses for the three and six months ended June 30, 2016, respectively, in connection with the research and development tax incentive from Australia. As of June 30, 2017 , and December 31, 2016 , the research and development tax incentive receivable was AUD 3.7 million ( $2.9 million ) and AUD 3.1 million ( $2.2 million), respectively. In March 2016, the Company received AUD 237,000 ( $181,000 ) for overseas findings and recorded the funds as deferred tax incentive in accrued expenses and other payables on the condensed consolidated balance sheet due to the possibility that the funds could have to be repaid. 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 were no longer deemed to be at risk of clawback and the Company recognized such amounts in December 2016 as a reduction of research and development expenses for the overseas findings received in 2016. SBIR Grant In May 2017, the Company was awarded a Phase 2 Small Business Innovation Research ("SBIR") Grant from the National Institute of Diabetes and Digestive and Kidney Diseases ("NIDDK") of the National Institutes of Health ("NIH") in support of research aimed at developing biomarkers that define IL-23R target engagement by oral peptide antagonists and the effects of that engagement of downstream signaling. The total grant award was $1.3 million and is for the period from May 2017 to April 2019. 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 pre-clinical 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 was for the period from August 2016 to January 2017. In September 2015, the Company was awarded a Phase 1 SBIR Grant from the NIDDK of the NIH in support of research on orally stable peptide antagonists of IL-23R as potential treatments for IBD. The total grant award was $224,000 and was for the period from September 2015 to August 2016. The Company recognizes a reduction to research and development expenses when expenses related to the grants have been incurred and the grant funds become contractually due from NIH. The Company recorded $20,000 as a reduction of research and development expenses for the three and six months ended June 30, 2017. The Company recorded $69,000 as a reduction of research and development expenses for the six months ended June 30, 2016. The Company recorded a receivable for $19,000 and $100,000 as of June 30, 2017 and December 31, 2016 , 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 condensed consolidated balance sheets.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies In March 2017, the Company entered into a lease agreement for office and laboratory space located in Newark, California. The Company relocated its operations to the new facility in May 2017. The Company provided the landlord with a $450,000 letter of credit collateralized by restricted cash as security deposit for the lease, which expires in May 2024. The Company is entitled to tenant improvement allowances of approximately $469,000 , any unused portion of which expires in December 2018. The Company records tenant improvement allowances as deferred rent when funds are received and associated capital expenditures as leasehold improvements that will be amortized over the shorter of their useful life or the remaining term of the lease. The following table summarizes the Company's minimum lease payments related to the Newark facility as of June 30, 2017 (in thousands): Year Ending December 31: Amount 2017 (remaining six months) $ 495 2018 1,667 2019 1,941 2020 1,999 2021 2,059 Thereafter 5,228 Total minimum lease payments $ 13,389

Preferred Stock Warrants

Preferred Stock Warrants	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Preferred Stock Warrants	Preferred Stock Warrants 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. 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 for the six months ended June 30, 2016, representing the increase in the fair value of the redeemable convertible preferred stock warrant liability in the condensed consolidated statements of operations. There were no such charges incurred for the three months ended June 30, 2016 and the three and six months ended June 30, 2017.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock Tranche Liability	6 Months Ended
	Jun. 30, 2017
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock Tranche Liability	Redeemable Convertible Preferred Stock Tranche Liability 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. 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. 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. The Company recorded a charge of $4.2 million for the increase in the fair value of the Series C redeemable convertible preferred stock liability in the condensed consolidated statements of operations for the six months ended June 30, 2016. There were no such charges incurred for the three months ended June 30, 2016 and the three and six months ended June 30, 2017.

Equity Plans

Equity Plans	6 Months Ended
	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Plans	Equity Plans Equity Incentive Plan In July 2016, the Company’s board of directors and stockholders approved the Company's 2016 Equity Incentive Plan (the “2016 Plan”) to replace the 2007 Stock Option Plan, which became effective upon the Company’s IPO. Under the 2016 Plan, 1,200,000 shares of the Company’s common stock were initially reserved for issuance of stock options, restricted stock units, and other awards to employees, directors, and consultants. Pursuant to the “evergreen” provision contained in the 2016 Plan, the number of shares reserved for issuance under the 2016 Plan automatically increases on January 1 of each year, starting on January 1, 2017 and continuing through (and including) January 1, 2026, by 4% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding fiscal year, or a lesser number of shares determined by the Company’s board of directors. As of June 30, 2017 , the Company has reserved 1,868,891 shares of common stock for issuance under the 2016 Plan. 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. Options granted under the 2016 Plan expire no later than ten years from the date of grant. Employee stock options generally vest over a period of four years. Non-employee director initial stock options generally vest over a period of three years, and non-employee director annual refresher stock options generally vest over a period of approximately one year. Stock Options Activity under the Company’s equity incentive plans is set forth below: Options Outstanding Options Available for Grant Options Outstanding Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value (1) (in thousands) Balances at December 31, 2016 164,328 2,393,829 $ 10.39 8.79 Additional options authorized 668,891 — Options granted (261,000 ) 261,000 $ 10.54 Options exercised — (151,299 ) $ 1.32 Options forfeited 50,271 (50,271 ) $ 18.91 Balances at June 30, 2017 622,490 2,453,259 $ 10.80 8.73 $ 10,463 Options exercisable at June 30, 2017 680,187 $ 8.20 8.22 $ 4,056 Options vested and expected to vest at June 30, 2017 2,453,259 $ 10.80 8.73 $ 10,463 ____________________ (1) The aggregate intrinsic values were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on June 30, 2017 . The calculation excludes options with an exercise price higher than the closing price of the Company's common stock on June 30, 2017 . During the six months ended June 30, 2017, the estimated weighted-average grant-date fair value of common stock underlying options granted was $6.26 per share. 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: Three Months Ended Six Months Ended 2017 2016 2017 2016 Expected term (in years) 5.50 - 6.07 5.88 5.50 - 6.08 5.88 - 5.94 Expected volatility 64.4% - 65.4% 62.5% 62.5% - 65.4% 62.5% - 64.8% Risk-free interest rate 1.88% - 1.98% 1.38% 1.88% - 2.07% 1.27% - 1.38% Dividend yield — — — — 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 closing of the IPO. Under the 2016 ESPP, 150,000 shares of the Company’s common stock were initially reserved for issuance for employee purchases of the Company’s common stock. Pursuant to the “evergreen” provision contained in the 2016 ESPP, the number of shares reserved for issuance under the 2016 ESPP automatically increases on January 1 of each year, starting on January 1, 2017 and continuing through (and including) January 1, 2026 by the lesser of (i) 1% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding fiscal year, (ii) 300,000 shares, or (iii) such other number of shares determined by the Company’s 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, eligible 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. As of June 30, 2017 , a total of 317,222 shares of common stock were authorized for issuance under the 2016 ESPP, and 25,682 shares have been issued. Stock-Based Compensation Total stock-based compensation expense was as follows (in thousands): Three Months Ended Six Months Ended 2017 2016 2017 2016 Research and development $ 476 $ 46 $ 799 $ 75 General and administrative 525 60 1,046 87 Total stock-based compensation expense $ 1,001 $ 106 $ 1,845 $ 162 As of June 30, 2017 , total unrecognized stock-based compensation expense related to stock options totaled $11.6 million , which the Company expects to recognize over a weighted-average period of approximately 2.71 years .

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders	6 Months Ended
	Jun. 30, 2017
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders As the Company had net losses for the three and six months ended June 30, 2017 and 2016 , all potential common shares were determined to be anti-dilutive. The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Three Months Ended Six Months Ended 2017 2016 2017 2016 Numerator: Net loss $ (14,979 ) $ (7,098 ) $ (29,080 ) $ (18,845 ) Accretion of redeemable convertible preferred stock — (225 ) — (265 ) Net loss attributable to common stockholders $ (14,979 ) $ (7,323 ) $ (29,080 ) $ (19,110 ) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 16,875,627 383,910 16,821,225 335,855 Net loss per share attributable to common stockholders, basic and diluted $ (0.89 ) $ (19.07 ) $ (1.73 ) $ (56.90 ) The following outstanding shares of potentially dilutive securities have been excluded from diluted net loss per share attributable to common stockholders computations for the three and six months ended June 30, 2017 and 2016 because their inclusion would be anti-dilutive: Three Months Ended Six Months Ended 2017 2016 2017 2016 Redeemable convertible preferred stock on an as-converted basis — 8,577,571 — 8,577,571 Options to purchase common stock 2,453,259 1,309,841 2,453,259 1,309,841 ESPP shares 23,262 — 23,262 — Total 2,476,521 9,887,412 2,476,521 9,887,412

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been condensed or omitted, and accordingly the consolidated balance sheet as of December 31, 2016 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete consolidated financial statements. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three and six months ended June 30, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017 or for any other interim period or for any other future year. The accompanying interim unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2016 included in the Company’s Annual Report on Form 10-K, filed with the SEC on March 7, 2017.
Principles of Consolidation	Principles of Consolidation The accompanying unaudited interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany transactions and balances have been eliminated upon consolidation.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with 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 condensed 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, 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 of the Company’s cash is held by two financial institutions that management believes are of high credit quality. Such deposits may, at times, exceed federally insured limits. The primary focus of the Company’s investment strategy is to preserve capital and to meet liquidity requirements. The Company’s cash equivalents and available-for-sale securities are managed by external managers within the guidelines of the Company’s investment policy. The Company’s investment policy addresses the level of credit exposure by limiting concentration in any one corporate issuer and establishing a minimum allowable credit rating. To manage its credit risk exposure, the Company maintains its portfolio of cash equivalents and available-for-sale securities in fixed income securities denominated and payable in U.S. dollars. Permissible investments of fixed income securities include obligations of the U.S. government and its agencies, money market instruments including commercial paper and negotiable certificates of deposit, and highly rated corporate debt obligations and money market funds. The Company has not experienced any material credit losses on its investments.
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.
Restricted Cash	Restricted Cash Restricted cash consists of cash balances primarily held as security in connection with the Company’s corporate credit card and a letter of credit related to the Company's facility lease entered into in March 2017. Cash as Reported in Consolidated Statements of Cash Flows Cash as reported in the unaudited condensed consolidated statements of cash flows includes the aggregate amounts of cash and cash equivalents and the restricted cash as presented on the consolidated balance sheets.
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 greater than three months but no longer than 365 days as of the balance sheet date. Long-term marketable securities have maturities of 365 days or longer 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 to all financial assets and liabilities that are recognized or disclosed at fair value in the condensed 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 approximates fair value due to their short-term maturities.
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 pre-clinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated services provided but not yet invoiced, and includes these costs in accrued expenses and other payables in the condensed consolidated balance sheets and within research and development expense in the condensed 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 at each balance sheet date. As actual costs become known, the Company adjusts its accrued liabilities. The Company has not experienced any material differences between accrued liabilities and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled, and the rate of patient enrollment 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.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred, unless there is an alternate future use in other research and development projects or otherwise. Research and development costs include salaries and benefits, stock-based compensation expense, laboratory supplies and facility-related overhead, outside contracted services including clinical trial costs, manufacturing and process development costs for both clinical and preclinical materials, research costs, development milestone payments under license and collaboration agreements, and other consulting services.
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. 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 annual turnover of less than AUD 20.0 million and cannot be controlled by income tax exempt entities. The research and development tax incentive is recognized as a reduction to 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% of 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 expense 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 to reflect that the funds are owed to the Company for the period the eligible costs are incurred.
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, if applicable. 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.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In November 2015, Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes , which is intended to simplify and improve how deferred income taxes are classified on the balance sheet. This guidance eliminates the current requirement to present deferred tax assets and liabilities as current and noncurrent in a classified balance sheet and now requires entities to classify all deferred tax assets and liabilities as noncurrent. The guidance is effective for annual periods beginning after December 15, 2016 and for interim periods within those annual periods, and early adoption is permitted. The Company adopted this guidance effective January 1, 2017. The adoption of this guidance did not have a material impact on the Company's financial position, results of operations or liquidity. In March 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, which is intended to simplify several aspects of accounting for employee share-based payment transactions, including 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 guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2016, and early adoption is permitted. The Company adopted this guidance effective January 1, 2017 and has elected to recognize forfeitures of share-based payment awards as they occur on a prospective basis. The impact of the adoption of ASU 2016-09 was not material to the Company’s condensed consolidated financial statements. The adoption of this guidance did not have a material impact on the income tax effects of share-based payment awards as the resulting change in the Company's deferred income tax assets is fully offset by a corresponding deferred income tax asset valuation allowance. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash , which requires the presentation of changes in restricted cash or restricted cash equivalents on the statement of cash flows. This guidance is effective for the fiscal years and interim periods within those years beginning after December 15, 2017, with early adoption permitted. The Company early adopted this guidance effective March 31, 2017, and, accordingly, amounts generally described as restricted cash are included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts of cash reflected on the accompanying consolidated statements of cash flows. The Company has adopted ASU 2016-18 retrospectively and has revised the prior period cash flows from investing activities, beginning cash balance, and ending cash balance to reflect the change in presentation of restricted cash. Other than the change in presentation in the accompanying consolidated statements of cash flows, the adoption of this guidance had no effect on the Company’s financial position, results of operations or liquidity. Recently Issued Accounting Pronouncements Not Adopted as of June 30, 2017 In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which amends the guidance for accounting for revenue from contracts with customers. In 2015 and 2016, the FASB issued additional ASUs that delayed the effective date and clarified various aspects of the new guidance, including principal vs. agent considerations, identifying performance obligations and licensing, and also included other improvements and practical expedients. The new standard will become effective for the Company on January 1, 2018, and early application is permitted for periods beginning on or after January 1, 2017. The new guidance applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under the new guidance, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of the new guidance, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company expects to modify its accounting policies to reflect the requirements of this guidance and expects to select the full retrospective transition method. The Company did not recognize revenue for the six months ended June 30, 2017 and 2016 and therefore, the planned adoption of this guidance will not affect the Company's consolidated financial statements and disclosures for these periods or future periods until the Company reports revenues. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) . Under the new guidance, (with the exception of short-term leases) at the commencement date, lessees will be required to recognize a lease liability and a right-of-use asset. Lessor accounting is largely unchanged, while lessees will no longer be provided with a source of off-balance sheet financing. This guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. Lessees (for capital and operating leases) are required to apply the modified retrospective transition method for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective method does not require any transition accounting for leases that did not exist before the earliest comparative period presented. While the Company continues to evaluate the impact of this guidance on its consolidated financial statements, it expects that its non-cancellable operating lease commitments will be subject to the new guidance and recognized as right-of-use assets and operating lease liabilities on the Company’s consolidated balance sheets, and that the adoption of this new guidance will not have a material impact on its results of operations or liquidity. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326) , which is intended to provide financial statement users with more useful information about expected credit losses on financial assets held by a reporting entity at each reporting date. The new standard replaces the existing incurred loss impairment methodology with a methodology that requires consideration of a broader range of reasonable and supportable forward-looking information to estimate all expected credit losses. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2019 and early adoption is permitted for fiscal years and interim periods within those years beginning after December 15, 2018. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , which clarifies the classification of certain cash receipts and cash payments in the statements of cash flow to eliminate the diversity in practice related to eight specific cash flow issues. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, and early adoption is permitted. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures. In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting, which provides guidance on the types of changes to the terms and conditions of share-based payment awards to which an entity would be required to apply modification accounting. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. This guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, and early adoption is permitted. The Company is currently evaluating the impact of this new guidance on its consolidated financial statements and disclosures.
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 —Inputs are unadjusted quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2— Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3 —Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. In determining fair value, the Company utilizes quoted market prices, broker or dealer quotations, or valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible and considers counterparty credit risk in its assessment of fair value.

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Schedule of Restricted Cash and Cash Equivalents	Cash as reported in the unaudited condensed consolidated statements of cash flows consists of (in thousands): June 30, 2017 2016 Cash and cash equivalents $ 10,365 $ 13,768 Restricted cash - current 10 10 Restricted cash - noncurrent 450 — Cash balance in condensed consolidated statements of cash flows $ 10,825 $ 13,778
Schedule of Cash and Cash Equivalents	Cash as reported in the unaudited condensed consolidated statements of cash flows consists of (in thousands): June 30, 2017 2016 Cash and cash equivalents $ 10,365 $ 13,768 Restricted cash - current 10 10 Restricted cash - noncurrent 450 — Cash balance in condensed consolidated statements of cash flows $ 10,825 $ 13,778

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2017
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 (in thousands). June 30, 2017 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 9,236 $ — $ — $ 9,236 Corporate bonds — 15,821 — 15,821 Commercial paper — 1,200 — 1,200 Government bonds — 37,106 — 37,106 Total financial assets $ 9,236 $ 54,127 $ — $ 63,363 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 Government bonds — 41,289 — 41,289 Total financial assets $ 11,270 $ 73,899 $ — $ 85,169

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2017
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): June 30, 2017 Amortized Cost Gross Unrealized Gains Losses Fair Value Money market funds $ 9,236 $ — $ — $ 9,236 Corporate bonds 15,839 — (18 ) 15,821 Commercial paper 1,200 — — 1,200 Government bonds 37,163 — (57 ) 37,106 Total cash equivalents and available-for-sale securities $ 63,438 $ — $ (75 ) $ 63,363 Classified as: Cash equivalents $ 9,236 Available-for-sale securities - current 54,127 Available-for-sale securities - noncurrent — Total cash equivalents and available-for-sale securities $ 63,363 December 31, 2016 Amortized Cost Gross Unrealized 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
Summary of Accrued Expenses and Other Payables	Accrued expenses and other payables consisted of the following (in thousands): June 30, 2017 December 31, 2016 Accrued clinical and research related expenses $ 4,299 $ 3,617 Accrued employee related expenses 1,338 1,420 Accrued professional service fees 669 115 Accrued milestone payment to former collaboration partner 250 — Other 171 120 Total accrued expenses and other payables $ 6,727 $ 5,272

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	The following table summarizes the Company's minimum lease payments related to the Newark facility as of June 30, 2017 (in thousands): Year Ending December 31: Amount 2017 (remaining six months) $ 495 2018 1,667 2019 1,941 2020 1,999 2021 2,059 Thereafter 5,228 Total minimum lease payments $ 13,389

Equity Plans (Tables)

Equity Plans (Tables)	6 Months Ended
	Jun. 30, 2017
Schedule of Activity under Stock Option Plan	Activity under the Company’s equity incentive plans is set forth below: Options Outstanding Options Available for Grant Options Outstanding Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value (1) (in thousands) Balances at December 31, 2016 164,328 2,393,829 $ 10.39 8.79 Additional options authorized 668,891 — Options granted (261,000 ) 261,000 $ 10.54 Options exercised — (151,299 ) $ 1.32 Options forfeited 50,271 (50,271 ) $ 18.91 Balances at June 30, 2017 622,490 2,453,259 $ 10.80 8.73 $ 10,463 Options exercisable at June 30, 2017 680,187 $ 8.20 8.22 $ 4,056 Options vested and expected to vest at June 30, 2017 2,453,259 $ 10.80 8.73 $ 10,463 ____________________ (1) The aggregate intrinsic values were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on June 30, 2017 . The calculation excludes options with an exercise price higher than the closing price of the Company's common stock on June 30, 2017 .
Schedule of Stock-based Compensation Expense for Employees and Non-employees for Stock Options and the 2016 ESPP	Total stock-based compensation expense was as follows (in thousands): Three Months Ended Six Months Ended 2017 2016 2017 2016 Research and development $ 476 $ 46 $ 799 $ 75 General and administrative 525 60 1,046 87 Total stock-based compensation expense $ 1,001 $ 106 $ 1,845 $ 162
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: Three Months Ended Six Months Ended 2017 2016 2017 2016 Expected term (in years) 5.50 - 6.07 5.88 5.50 - 6.08 5.88 - 5.94 Expected volatility 64.4% - 65.4% 62.5% 62.5% - 65.4% 62.5% - 64.8% Risk-free interest rate 1.88% - 1.98% 1.38% 1.88% - 2.07% 1.27% - 1.38% Dividend yield — — — —

Net Loss per Share Attributab25

Net Loss per Share Attributable to Common Stockholders (Tables)	6 Months Ended
	Jun. 30, 2017
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 basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Three Months Ended Six Months Ended 2017 2016 2017 2016 Numerator: Net loss $ (14,979 ) $ (7,098 ) $ (29,080 ) $ (18,845 ) Accretion of redeemable convertible preferred stock — (225 ) — (265 ) Net loss attributable to common stockholders $ (14,979 ) $ (7,323 ) $ (29,080 ) $ (19,110 ) Denominator: Weighted-average shares used to compute net loss per common share, basic and diluted 16,875,627 383,910 16,821,225 335,855 Net loss per share attributable to common stockholders, basic and diluted $ (0.89 ) $ (19.07 ) $ (1.73 ) $ (56.90 )
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 attributable to common stockholders computations for the three and six months ended June 30, 2017 and 2016 because their inclusion would be anti-dilutive: Three Months Ended Six Months Ended 2017 2016 2017 2016 Redeemable convertible preferred stock on an as-converted basis — 8,577,571 — 8,577,571 Options to purchase common stock 2,453,259 1,309,841 2,453,259 1,309,841 ESPP shares 23,262 — 23,262 — Total 2,476,521 9,887,412 2,476,521 9,887,412

Organization and Description 26

Organization and Description of Business - Additional Information (Detail) $ / shares in Units, $ in Thousands	Aug. 16, 2016$ / sharesshares	Sep. 30, 2016$ / sharesshares	Jul. 31, 2016	Sep. 30, 2016USD ($)$ / shares	Jun. 30, 2017USD ($)	Dec. 31, 2016USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit | $					$ 93,673	$ 64,593
Subsidiary, Sale of Stock [Line Items]
Stock split, conversion ratio			0.0689655
IPO [Member]
Subsidiary, Sale of Stock [Line Items]
Stock issued during period, shares, new issues | shares	7,500,000	252,972
Shares issued, price per share (in usd per share) | $ / shares	$ 12	$ 12		$ 12
Proceeds from issuance initial public offering | $				$ 83,600
Common Stock [Member] | IPO [Member]
Subsidiary, Sale of Stock [Line Items]
Convertible preferred stock, shares issued upon conversion | shares	8,577,571

Summary of Significant Accoun27

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Restricted Cash [Abstract]
Cash and cash equivalents	$ 10,365	$ 21,084	$ 13,768
Restricted cash - current	10	10	10
Restricted cash - noncurrent	450	0	0
Cash balance in condensed consolidated statements of cash flows	$ 10,825	$ 21,094	$ 13,778	$ 4,065

Janssen Collaboration Agreeme28

Janssen Collaboration Agreement (Details) - Collaborative Arrangement, Product [Member] - USD ($)	3 Months Ended
	Sep. 30, 2017	Jun. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement, percentage of development costs incurred		20.00%
Janssen Biotech, Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement, percentage of development costs incurred		80.00%
Janssen Biotech, Inc. [Member] | Scenario, Forecast [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Nonrefundable upfront payment	$ 50,000,000
Revenue recognition, milestone method, revenue recognized	$ 615,000,000
Collaboration agreement, detail capital required for commercial launch, percent (up to)	30.00%
First Opt-in [Member] | Janssen Biotech, Inc. [Member] | Scenario, Forecast [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in payment eligible to receive under collaboration arrangement	$ 125,000,000
Second Opt-in [Member] | Janssen Biotech, Inc. [Member] | Scenario, Forecast [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in payment eligible to receive under collaboration arrangement	$ 200,000,000

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 63,363	$ 85,169
Corporate Bonds Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	15,821	21,841
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	9,236	11,270
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	1,200	10,769
Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	37,106	41,289
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	9,236	11,270
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	9,236	11,270
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	54,127	73,899
Level 2 [Member] | Corporate Bonds Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	15,821	21,841
Level 2 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	1,200	10,769
Level 2 [Member] | Government Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 37,106	$ 41,289

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Cash Equivalents and Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	$ 63,438	$ 85,241
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	2
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(75)	(74)
Total cash equivalents and available-for-sale securities, Fair Value	63,363	85,169
Cash equivalents	9,236	18,504
Available-for-sale securities - current	54,127	56,515
Available-for-sale securities - noncurrent	0	10,150
Total cash equivalents and available-for-sale securities, Fair Value	63,363	85,169
Corporate Bonds Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	15,839	21,886
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	0
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(18)	(45)
Total cash equivalents and available-for-sale securities, Fair Value	15,821	21,841
Total cash equivalents and available-for-sale securities, Fair Value	15,821	21,841
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	9,236	11,270
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	0
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	0	0
Total cash equivalents and available-for-sale securities, Fair Value	9,236	11,270
Total cash equivalents and available-for-sale securities, Fair Value	9,236	11,270
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	1,200	10,769
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	0
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	0	0
Total cash equivalents and available-for-sale securities, Fair Value	1,200	10,769
Total cash equivalents and available-for-sale securities, Fair Value	1,200	10,769
Government Bonds [Member]
Cash and Cash Equivalents [Line Items]
Total cash equivalents and available-for-sale securities, Amortized Cost	37,163	41,316
Total cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	2
Total cash equivalents and available-for-sale securities, Gross Unrealized Losses	(57)	(29)
Total cash equivalents and available-for-sale securities, Fair Value	37,106	41,289
Total cash equivalents and available-for-sale securities, Fair Value	$ 37,106	$ 41,289

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Realized gains or losses on available-for-sale securities	$ 0	$ 0

Balance Sheet Components - Su32

Balance Sheet Components - Summary of Accrued Expenses and Other Payables (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued clinical and research related expenses	$ 4,299	$ 3,617
Accrued employee related expenses	1,338	1,420
Accrued professional service fees	669	115
Accrued milestone payment to former collaboration partner	250	0
Other	171	120
Total accrued expenses and other payables	$ 6,727	$ 5,272

Research Collaboration and Li33

Research Collaboration and License Agreement - Additional Information (Detail) - Research Collaboration and License Agreement [Member] - PTG-300 [Member] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment based on agreement		$ 250,000
Milestone payment upon contractual obligation	$ 250,000
Term (in years)			10 years
Development Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate milestone payment			$ 28,500,000
Sales Milestones [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate milestone payment			$ 100,000,000

Government Programs - Additiona

Government Programs - Additional Information (Detail) AUD in Thousands

1 Months Ended

3 Months Ended

6 Months Ended

May 31, 2017USD ($)

Jul. 31, 2016USD ($)

Mar. 31, 2016USD ($)

Mar. 31, 2016AUD

Sep. 30, 2015USD ($)

Jun. 30, 2017USD ($)

Jun. 30, 2017AUD

Jun. 30, 2016USD ($)

Jun. 30, 2016AUD

Jun. 30, 2017USD ($)

Jun. 30, 2017AUD

Jun. 30, 2016USD ($)

Jun. 30, 2016AUD

Jun. 30, 2017AUD

Dec. 31, 2016USD ($)

Dec. 31, 2016AUD

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Research and development tax incentive receivable

$ 2,881,000

$ 2,881,000

$ 2,241,000

SBIR Grant [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Reduction of research and development expenses related to tax

20,000

20,000

$ 69,000

Research and development grants

$ 1,300,000

$ 219,000

$ 224,000

Grants receivable

19,000

19,000

100,000

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

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Research and development tax incentive receivable

2,900,000

2,900,000

AUD 3,700

$ 2,200,000

AUD 3,100

Deferred tax incentive

$ 181,000

AUD 237

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

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Reduction of research and development expenses related to tax

$ 377,000

AUD 501

$ 498,000

AUD 666

$ 480,000

AUD 635

$ 1,000,000

AUD 1,400

Lease Agreement - Additional In

Lease Agreement - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2017 (remaining six months)	$ 495
2,018	1,667
2,019	1,941
2,020	1,999
2,021	2,059
Thereafter	5,228
Total minimum lease payments	13,389
Newark, California [Member]
Operating Leased Assets [Line Items]
Letter of credit, outstanding amount	450
Tenant improvement allowances	$ 469

Preferred Stock Warrants - Addi

Preferred Stock Warrants - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	May 31, 2016
Class of Warrant or Right [Line Items]
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants				$ 0	$ 22,508
Remeasured fair value of warrants	$ 1,000
Reclassification of redeemable convertible preferred stock warrant liability to redeemable convertible preferred stock				0	1,005
Change in fair value of redeemable convertible preferred stock warrant liability		$ 0	$ 0	$ 0	$ 525
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
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%
Series B Redeemable Convertible Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Redeemable convertible preferred stock, shares issued	1,999,998
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants	$ 20
Number of redeemable convertible preferred stock expired unexercised						2,000,000

Redeemable Convertible Prefer37

Redeemable Convertible Preferred Stock Tranche Liability (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 10, 2015	Apr. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jul. 31, 2015
Temporary Equity [Line Items]
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants						$ 0	$ 22,508
Settlement of fair value of redeemable convertible preferred stock liability			$ 5,800			0	5,837
Change in fair value associated with redeemable convertible preferred stock tranche liability						0	4,194
Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued	45,189,794
Redeemable convertible preferred stock, price per share								$ 0.4979
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants	$ 17,500		$ 22,500
Fair value of redeemable convertible preferred stock liability	$ 1,000				$ 5,800		5,800
Change in fair value associated with redeemable convertible preferred stock tranche liability				$ 0	$ 0	$ 0	$ 4,200
Maximum [Member] | Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued	35,147,617							80,337,411
Second Tranche Warrants [Member] | Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Additional shares to be issued upon the achievement of certain development milestones					45,189,794		45,189,794
Option Pricing Model [Member]
Temporary Equity [Line Items]
Percentage of weighted value per share		67.00%
Option Pricing Model [Member] | Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Percentage of weighted value per share			67.00%
PWERM [Member]
Temporary Equity [Line Items]
Percentage of weighted value per share		33.00%
PWERM [Member] | Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Percentage of weighted value per share			33.00%

Equity Plans - Additional Infor

Equity Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	6 Months Ended
	Jul. 31, 2016	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, weighted-average grant-date fair value		$ 6.26
Total unrecognized stock-based compensation costs related to stock options		$ 11.6
Period of unrecognized stock-based compensation costs to be recognized		2 years 8 months 16 days
2016 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	1,200,000	1,868,891
Percentage of outstanding stock maximum		4.00%
2016 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
2016 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	150,000	317,222
Percentage of outstanding stock maximum		1.00%
Additional shares issuable maximum	300,000
Percentage of discount from fair market value of common stock on offering date	85.00%
Shares issued in period		25,682
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%
Employee Stock Option [Member] | 2016 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional vesting years		4 years
Non-employee Director Initial Stock Options [Member] | 2016 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional vesting years		3 years
Non-employee Director Annual Refresher Stock Options [Member] | 2016 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional vesting years		1 year

Equity Plans - Schedule of Acti

Equity Plans - Schedule of Activity under Stock Option Plan (Detail) - 2007 Stock Option Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options Granted [Roll Forward]
Options Available for Grant, Beginning balance	164,328
Options Available for Grant, Number of Additional Shares Authorized	668,891
Options Available for Grant, Options granted	(261,000)
Options Available for Grant, Options exercised	0
Options Available for Grant, Options Forfeited	50,271
Options Available for Grant, Ending balance	622,490	164,328
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options Outstanding, Beginning balance	2,393,829
Number of Options Outstanding, Options granted	261,000
Number of Options Outstanding, Options exercised	(151,299)
Number of Options Outstanding, Options Forfeited	(50,271)
Number of Options Outstanding, Ending balance	2,453,259	2,393,829
Number of Options Outstanding, Options exercisable	680,187
Number of Options Outstanding, Options vested and expected to vest	2,453,259
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price Per Share, Beginning balance	$ 10.39
Weighted-Average Exercise Price Per Share, Options granted	10.54
Weighted-Average Exercise Price Per Share, Options exercised	1.32
Weighted Average Exercise Price, Options Forfeited	18.91
Weighted-Average Exercise Price Per Share, Ending balance	10.80	$ 10.39
Weighted-Average Exercise Price Per Share, Options exercisable	8.20
Weighted-Average Exercise Price Per Share, Options vested and expected to vest	$ 10.80
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-Average Remaining Contractual Life (years)	8 years 8 months 23 days	8 years 9 months 15 days
Weighted-Average Remaining Contractual Life (years), Options exercisable	8 years 2 months 19 days
Weighted-Average Remaining Contractual Life (years), Options vested and expected to vest	8 years 8 months 23 days
Aggregate Intrinsic Value, Options Outstanding	$ 10,463
Aggregate Intrinsic Value, Options exercisable	4,056
Aggregate Intrinsic Value, Options vested and expected to vest	$ 10,463

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)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		5 years 10 months 17 days
Expected volatility		62.50%
Risk-free interest rate		1.38%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 26 days		6 years 29 days	5 years 11 months 9 days
Expected volatility	65.40%		65.40%	64.80%
Risk-free interest rate	1.98%		2.07%	1.38%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months		5 years 6 months	5 years 10 months 17 days
Expected volatility	64.40%		62.50%	62.50%
Risk-free interest rate	1.88%		1.88%	1.27%

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	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,001	$ 106	$ 1,845	$ 162
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	476	46	799	75
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 525	$ 60	$ 1,046	$ 87

Net Loss per Share Attributab42

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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (14,979)	$ (7,098)	$ (29,080)	$ (18,845)
Accretion of redeemable convertible preferred stock	0	(225)	0	(265)
Net loss attributable to common stockholders	$ (14,979)	$ (7,323)	$ (29,080)	$ (19,110)
Denominator:
Weighted-average shares used to compute net loss per common share, basic and diluted	16,875,627	383,910	16,821,225	335,855
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.89)	$ (19.07)	$ (1.73)	$ (56.90)

Net Loss per Share Attributab43

Net Loss per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share	2,476,521	9,887,412	2,476,521	9,887,412
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		8,577,571		8,577,571
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	2,453,259	1,309,841	2,453,259	1,309,841
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share	23,262	0	23,262	0