0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Interest Expense (Detail) - 0.25% Convertible Senior Notes Due 2022 [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Debt Instrument [Line Items]
Contractual interest expense	$ 250	$ 250
Amortization of debt discount	5,307	4,894
Amortization of issuance costs	396	366
Total interest expense	$ 5,953	$ 5,510