Convertible Notes, Net - Summary of Details of Net Book Value of Convertible Note (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Deferred financing costs	$ (21,790)	$ (16,681)
Net book value	778,070	563,911
Convertible Senior Note [Member]
Debt Instrument [Line Items]
Face Value	795,000	575,000
Unamortized discount	(15,848)	(10,279)
Deferred financing costs	(1,082)	(810)
Net book value	$ 778,070	$ 563,911