Deferred Costs - Summary of Deferred Costs and Amortization of Deferred Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Deferred Costs [Abstract]
Balance, beginning of period	$ 46,649	$ 45,528	$ 46,941	$ 45,475
Incurred deferred costs	14,258	12,676	39,329	36,888
Amortized deferred costs	(12,774)	(12,623)	(38,137)	(36,782)
Balance, end of period	$ 48,133	$ 45,581	$ 48,133	$ 45,581