Convertible Notes - Schedule of Interest Expenses Schedule of Interest Expenses Related to Convertible Notes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Contractual coupon interest	$ 1,643		$ 5,669
Amortization of discount	10,317	$ 9,843	2,180
Convertible Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Contractual coupon interest	22,929	23,750	5,302
Amortization of discount	7,863	7,468	2,152
Amortization of direct issue costs	2,454	2,375	28
Total	$ 33,246	$ 33,593	$ 7,482