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Collaboration and License Agreements - Janssen Pharmaceuticals, Inc - Additional Information (Detail)		1 Months Ended	3 Months Ended
	Oct. 03, 2018 USD ($) Obligation	Oct. 31, 2018 USD ($) Target $ / shares shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock			$ 60,521,729
Revenues			34,657,896	$ 3,509,821
Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price	$ 197,800,000
JJDC \| Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued \| shares		3,260,869
Stock issued, price per share \| $ / shares		$ 23.00
Janssen and JJDC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues			34,700,000
Contract assets			3,200,000
Contract liabilities			$ 158,100,000
Janssen and JJDC \| Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued \| shares		3,260,869
Stock issued, price per share \| $ / shares		$ 23.00
Proceeds from the issuance of common stock		$ 75,000,000
Janssen and JJDC \| Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock		75,000,000
Cash received as due under collaboration agreement		175,000,000
Janssen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of distinct performance obligations \| Obligation	1
Janssen \| Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments		$ 1,600,000,000
Janssen \| Research Collaboration and Option Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Number of additional targets for development, regulatory and sales milestone payments \| Target		3
Janssen \| Collaboration Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments		$ 1,900,000,000