Debt - Interest Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Convertible Notes [Member]
Debt Instrument [Line Items]
Interest expense—stated coupon rate	$ 3,292	$ 2,456
Interest expense—amortization of debt discount	2,278	1,755
Total interest expense—convertible notes	5,570	4,211
Cabot and Marlin Acquisitions [Member]
Debt Instrument [Line Items]
Interest expense—stated coupon rate	23,850	19,255
Interest expense—amortization of debt discount	(2,547)	(2,232)
Total interest expense—convertible notes	$ 21,303	$ 17,023