Summary of Convertible Debt (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Convertible Notes, net of unamortized deferred offering costs		$ 22,478	$ 0
Convertible Notes, net of unamortized discount and deferred offering costs		660,761	662,286
Total convertible debt, net		683,239	662,286
Convertible Notes, fair value		956,933	1,147,301
Convertible Notes due 2017
Debt Instrument [Line Items]
Convertible Notes		22,503	31,430
Convertible debt, Unamortized deferred offering costs		(25)	(110)
Convertible Notes, net of unamortized deferred offering costs		22,478	31,320
Convertible Notes, fair value	[1]	90,977	162,016
Convertible Notes due 2020
Debt Instrument [Line Items]
Convertible Notes		374,993	374,993
Convertible debt, unamortized discount		(53,239)	(65,478)
Convertible debt, Unamortized deferred offering costs		(4,923)	(6,210)
Convertible Notes, net of unamortized discount and deferred offering costs		316,831	303,305
Convertible Notes, fair value	[1]	442,754	502,701
Convertible Notes due 2018
Debt Instrument [Line Items]
Convertible Notes		374,980	374,980
Convertible debt, unamortized discount		(27,566)	(41,904)
Convertible debt, Unamortized deferred offering costs		(3,484)	(5,415)
Convertible Notes, net of unamortized discount and deferred offering costs		343,930	327,661
Convertible Notes, fair value	[1]	$ 423,202	$ 482,584

[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.