Deferred Costs - Summary of Deferred Costs and Amortization of Deferred Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs [Abstract]
Balances, at beginning of period	$ 39,933	$ 32,117
Incurred deferred costs	49,583	44,628
Amortized deferred costs	(44,041)	(36,812)
Balances, at end of period	$ 45,475	$ 39,933