Exchangeable Senior Notes - Summary of Amount of Interest Cost Recognized Relating to Contractual Interest Rates and Amortization of Discounts on Liability Components of Notes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Debt Disclosure [Abstract]
Contractual interest	$ 4,867	$ 1,972	$ 14,616	$ 4,940
Amortization of discount	1,243	805	3,716	2,198
Total interest expense recognized	$ 6,110	$ 2,777	$ 18,332	$ 7,138