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
	Mar. 31, 2017	Mar. 31, 2016
Debt Disclosure [Abstract]
Contractual interest	$ 4,867	$ 4,882
Amortization of discount	1,269	1,233
Total interest expense recognized	$ 6,136	$ 6,115