License and Collaboration Agreements - Additional Information (Detail) - USD ($)				3 Months Ended
	Apr. 04, 2019	Feb. 27, 2019	May 03, 2018	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018
Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Final exercise price		$ 165,000,000
Additional transaction fees		8,700,000
Additional development milestone payments to be paid		$ 200,000,000
Myonexus Therapeutics, Inc. [Member] | Scenario Forecast [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
In-process research and development expense				$ 168,700,000
Myonexus Therapeutics, Inc. [Member] | Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Date of acquisition	Apr. 04, 2019
Warrant Agreement [Member] | Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front cash payment under agreements			$ 60,000,000
Cash consideration under agreement excluding contingent payments			$ 200,000,000
License and Collaboration Agreements [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestone and up-front payments recognized as research and development expense					$ 1,100,000	$ 0
License and Collaboration Agreements [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory, commercial milestone and up-front royalty payments					$ 555,800,000