Debt - Interest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Convertible Notes [Member]
Debt Instrument [Line Items]
Interest expense—stated coupon rate	$ 3,315	$ 3,316	$ 9,915	$ 9,080
Interest expense—amortization of debt discount	2,359	2,228	6,947	6,164
Total interest expense—convertible notes	5,674	5,544	16,862	15,244
Cabot and Marlin Acquisitions [Member]
Debt Instrument [Line Items]
Interest expense—stated coupon rate	24,394	26,239	72,395	72,099
Interest expense—amortization of debt discount	(2,771)	(2,760)	(7,978)	(7,565)
Total interest expense—convertible notes	$ 21,623	$ 23,479	$ 64,417	$ 64,534