Convertible Senior Notes (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2014	Jul. 31, 2013
Debt Instrument [Line Items]
Convertible senior notes, principal amount	$ 167,727	$ 206,865
Convertible senior notes, debt issuance costs	3,173	3,858
Convertible senior notes, net of debt issuance costs	164,554	203,007
4.25% Convertible Senior Notes (due 2018)
Debt Instrument [Line Items]
Convertible senior notes, principal amount	54,727	93,865		$ 100,000
Convertible senior notes, debt issuance costs	610	1,098
Convertible senior notes, net of debt issuance costs	54,117	92,767
4.875% Convertible Senior Notes (due 2020)
Debt Instrument [Line Items]
Convertible senior notes, principal amount	113,000	113,000	$ 115,000
Convertible senior notes, debt issuance costs	2,563	2,760
Convertible senior notes, net of debt issuance costs	$ 110,437	$ 110,240