Debt - Schedule of Net Carrying Amount of Liability and Equity Components of Notes (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Liability component:
Principal	$ 690,000	$ 690,000
Unamortized debt discount	(89,500)	(106,224)
Unamortized transaction costs	(11,223)	(13,320)
Net carrying amount	589,277	570,456
Equity component, net of transaction costs	$ 114,938	$ 114,938