Property and Equipment - Depreciation and Amortization on Property and Equipment Using the Straight-Line Method (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Office furniture and fixtures	$ 1,551	$ 1,168
Software	3,068	2,146
Equipment	4,390	4,071
Leasehold improvements	1,720	1,617
Gross property and equipment	10,729	9,002
Less accumulated depreciation and amortization	(6,493)	(5,432)
Property and equipment, net	$ 4,236	$ 3,570