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 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	$ 0.3	$ 0.2	$ 0.7	$ 0.6
Plan name			401(K) plan