Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Sale Of Subsidiary [Abstract]
Defined contribution plan employer matching contribution percent for three percent of employee contribution	100.00%
Initial employee salary percentage with full employer contribution	3.00%
Defined contribution plan employer matching contribution percent for two percent of employee contribution	50.00%
Additional employee salary percentage with partly employer contribution	2.00%
Company's contributions to Plan	$ 1.3	$ 1.1	$ 1.0