Debt - Additional Information (Detail) - USD ($) $ in Thousands, shares in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2015	Jun. 30, 2015	Jun. 30, 2014
Debt Instrument [Line Items]
Total consideration for repurchase of warrants		$ 154,681	$ 50,775
3.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Warrants repurchased	4.7
Total consideration for repurchase of warrants	$ 154,700	154,700
Gain (loss) on change in the fair value of the derivative liability	$ (20,200)	$ (20,200)