Stock-Based Compensation - Summary of Stock Option Activity under Company's Stock Option Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance	344,090
Options Outstanding, Granted	20,000
Options Outstanding, Exercised	(178,090)
Options outstanding, ending balance	186,000	344,090
Options Outstanding, Options exercisable	166,000
Options Outstanding, Options vested or expected to vest	184,108
Weighted-Average Exercise Price Per Share, Options outstanding, beginning balance	$ 6.41
Weighted-Average Exercise Price Per Share, Granted	28.42
Weighted-Average Exercise Price Per Share, Exercised	5.64
Weighted- Average Exercise Price Per Share, Options outstanding, ending balance	9.50	$ 6.41
Weighted- Average Exercise Price Per Share, Options exercisable	7.22
Weighted-Average Exercise Price Per Share, Options vested or expected to vest	$ 9.31
Weighted-Average Remaining Contractual Term in Years, Options outstanding	4 years 3 months 25 days
Weighted-Average Remaining Contractual Term in Years, Options exercisable	3 years 8 months 12 days
Weighted-Average Remaining Contractual Term in Years, Options vested or expected to vest	4 years 3 months 3 days
Aggregate Intrinsic Value, Exercised	$ 2,704	$ 900	$ 1,900
Aggregate Intrinsic Value, Options outstanding	828
Aggregate Intrinsic Value, Options exercisable	828
Aggregate Intrinsic Value, Options vested or expected to vest	$ 828