Summary of Interest Expense on Debt (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Interest Expenses [Line Items]
Total interest expense on convertible debt	$ 23,460	$ 43,664	$ 42,707
Convertible Senior Notes
Schedule Of Interest Expenses [Line Items]
Coupon interest	4,907	12,452	10,407
Amortization of debt issuance costs	2,031	3,610	3,725
Accretion of discount on convertible notes	15,917	27,602	28,575
Total interest expense on convertible debt	$ 22,855	$ 43,664	$ 42,707