Convertible Notes, Net - Summary of Details of Net Book Value of Convertible Note (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Deferred financing costs	$ (16,681)	$ (15,272)
Net book value	563,911	166,762
Convertible Senior Note [Member]
Debt Instrument [Line Items]
Face Value	575,000	172,500
Unamortized discount	(10,279)	(5,532)
Deferred financing costs	(810)	(206)
Net book value	$ 563,911	$ 166,762