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, 2019	Mar. 31, 2018
Debt Disclosure [Abstract]
Contractual interest	$ 4,492	$ 4,561
Amortization of discount	1,162	1,209
Total interest expense recognized	$ 5,654	$ 5,770