Development Derivative Liability - Schedule of Development Derivative Liability (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance at fair market value	$ 223,245	$ 134,839	$ 60,736		$ 134,839
Amounts received under the SFJ agreement and SFJ amendment		20,000	40,000	$ 60,000
Gain/(loss) recorded in loss from remeasurement of development derivative liability	(2,770)	68,406	9,104	736	65,636	$ 9,840
Balance at fair market value	$ 220,475	$ 223,245	$ 109,840	$ 60,736	$ 220,475	$ 109,840