Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Pension Plans And Defined Benefit Postretirement Plans Disclosure [Abstract]
Matching contribution by the company to the plan	100.00%
Percentage of employees' eligible compensation	6.00%
Defined contribution plan, general and administrative expenses	$ 0.2	$ 0.2
Plan name	401(K) plan