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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Disclosure [Abstract]
Contractual interest	$ 4,492	$ 4,492	$ 8,984	$ 13,476
Amortization of discount	1,233	1,186	3,675	3,533
Total interest expense recognized	$ 5,725	$ 5,678	$ 12,659	$ 17,009