Debt - Balances of Liability and Equity Components (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Liability component—principal amount	$ 448,500	$ 448,500
Unamortized debt discount	(39,440)	(41,867)
Liability component—net carrying amount	409,060	406,633
Equity component	$ 58,950	$ 58,184