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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Disclosure [Abstract]
Contractual interest	$ 4,867	$ 4,867	$ 9,734	$ 9,749
Amortization of discount	1,290	1,240	2,559	2,473
Total interest expense recognized	$ 6,157	$ 6,107	$ 12,293	$ 12,222