Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Company's contributions to the plan	$ 2,500	$ 1,600	$ 1,200
Deferral percentage of base salary (up to)	80.00%
Deferral percentage of other compensation (up to)	100.00%
Employee deferrals deemed vested percentage upon contribution	100.00%
Company's contributions to the deferred compensation plan	$ 29