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Payment received for license agreement.

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Significant accounting policies line items.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Summary of Significant Accounting Policies - Additional Information (Detail)		1 Months Ended	12 Months Ended
	Mar. 09, 2018	Oct. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Reverse stock split			the Company effected a reverse split of all shares of its common and preferred stock at a ratio of 1-for-3.96
Reverse stock split ratio	0.2525
Number of operating segments \| Segment			1
Number of reportable segments \| Segment			1
Accumulated deficit			$ (205,326,000)	$ (122,828,000)
Minimum
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives			1 year
Impairment charges			$ 0	0
Maximum
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives			5 years
Taiho Agreement \| Taiho Pharmaceutical Co Ltd
Significant Accounting Policies [Line Items]
Accumulated deficit				2,200,000
Non-refundable upfront research and development fees term			5 years
Transaction price						$ 35,000,000
Non refundable and non creditable upfront cash payment received			$ 35,000,000
Payment received for license agreement		$ 5,000,000	5,000,000	5,000,000	$ 25,000,000
Additional payment to be received for license agreement			$ 5,000,000	5,000,000
Net reduction to deferred revenue				$ 2,200,000
Estimated performance period			5 years	4 years	5 years
Before Adoption of Topic 606
Significant Accounting Policies [Line Items]
Accumulated deficit				$ (122,828,000)
Before Adoption of Topic 606 \| Taiho Agreement \| Taiho Pharmaceutical Co Ltd
Significant Accounting Policies [Line Items]
Additional payment to be received for license agreement				$ 5,000,000
Non-refundable, non-creditable cash payment received					$ 25,000,000
ASC 606
Significant Accounting Policies [Line Items]
Accumulated deficit						(120,616,000)
Non-refundable upfront research and development fees term			5 years
ASC 606 \| Adjustment due to The Adoption of Topic 606
Significant Accounting Policies [Line Items]
Accumulated deficit						$ 2,212,000