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Key Component of Convertible Senior Notes (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
4.50% Convertible senior notes (due 2014)      
Debt Instrument [Line Items]      
Contractual interest expense on the coupon     $ 1,463
Amortization of debt discount and debt issuance costs recognized as interest expense     1,140
Amortization of Deferred Charges, Total     2,603
4.25% Convertible Senior Notes (due 2018)      
Debt Instrument [Line Items]      
Contractual interest expense $ 4,191 $ 4,250 4,250
Amortization of debt discount and debt issuance costs recognized as interest expense 1,172 836 835
Amortization of Deferred Charges, Total 5,363 5,086 5,085
4.875% Convertible Senior Notes (due 2020)      
Debt Instrument [Line Items]      
Contractual interest expense 5,508 5,606 3,135
Amortization of debt discount and debt issuance costs recognized as interest expense 804 811 473
Amortization of Deferred Charges, Total $ 6,312 $ 6,417 $ 3,608