Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Employee deferrals deemed vested percentage upon contribution			100.00%
Defined contribution plan, cost	$ 0.9	$ 0.6	$ 2.4	$ 1.9
Maximum
Defined Benefit Plan Disclosure [Line Items]
Deferral percentage of base salary (up to)			80.00%
Deferral percentage of other compensation (up to)			100.00%