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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt Disclosure [Abstract]
Contractual interest	$ 4,492	$ 4,492	$ 8,984	$ 8,984
Amortization of discount	1,233	1,185	2,442	2,347
Total interest expense recognized	$ 5,725	$ 5,677	$ 11,426	$ 11,331