Debt - Balances of Liability and Equity Components (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Debt Disclosure [Abstract]
Liability component—principal amount	$ 448,500	$ 287,500
Unamortized debt discount	(53,461)	(42,240)
Liability component—net carrying amount	395,039	245,260
Equity component	$ 54,523	$ 46,954