Summary of Convertible Debt (Detail) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term Convertible Notes, net of unamortized discount and deferred offering costs		$ 662,286	$ 642,902
Convertible Notes, fair value		1,147,301	1,079,792
Convertible Notes due 2020
Debt Instrument [Line Items]
Long-term Convertible Notes		374,993	375,000
Long-term convertible debt, unamortized discount		(65,478)	(77,045)
Long-term convertible debt, Unamortized deferred offering costs		(6,210)	(7,493)
Long-term Convertible Notes, net of unamortized discount and deferred offering costs		303,305	290,462
Convertible Notes, fair value	[1]	502,701	456,360
Convertible Notes due 2018
Debt Instrument [Line Items]
Long-term Convertible Notes		374,980	375,000
Long-term convertible debt, unamortized discount		(41,904)	(55,537)
Long-term convertible debt, Unamortized deferred offering costs		(5,415)	(7,335)
Long-term Convertible Notes, net of unamortized discount and deferred offering costs		327,661	312,128
Convertible Notes, fair value	[1]	482,584	442,448
Convertible Notes due 2017
Debt Instrument [Line Items]
Long-term Convertible Notes		31,430	40,558
Long-term convertible debt, Unamortized deferred offering costs		(110)	(246)
Long-term Convertible Notes, net of unamortized discount and deferred offering costs		31,320	40,312
Convertible Notes, fair value	[1]	$ 162,016	$ 180,984

[1] The fair value of the Company’s fixed rate convertible debt is based on open market trades and is classified as Level 1 in the fair value hierarchy.