Debt - Key Component of Convertible Senior Notes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Amortization of debt issuance costs recognized as interest expense	$ 1,077	$ 0	$ 0
3.25% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Contractual interest expense	899	0	0
Amortization of debt issuance costs recognized as interest expense	0	0	0
Interest Expense, Debt, Total	899	0	0
4.875% Convertible Senior Notes Due 2020
Debt Instrument [Line Items]
Contractual interest expense	3,370	5,509	5,509
Amortization of debt issuance costs recognized as interest expense	460	789	789
Interest Expense, Debt, Total	3,830	6,298	6,298
4.25% Convertible Senior Notes Due 2018
Debt Instrument [Line Items]
Contractual interest expense	0	373	2,184
Amortization of debt issuance costs recognized as interest expense	0	103	844
Interest Expense, Debt, Total	0	476	3,028
3.25% Convertible Senior Notes Due 2020
Debt Instrument [Line Items]
Contractual interest expense	580	815	103
Amortization of debt issuance costs recognized as interest expense	0	0	0
Interest Expense, Debt, Total	$ 580	$ 815	$ 103