Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 7,963	$ 7,256
Less accumulated depreciation and amortization	(5,241)	(4,460)
Property and equipment, net	2,722	2,796
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,903	1,854
Property and equipment, useful life in years	5 years
Systems Hardware
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,714	1,623
Property and equipment, useful life in years	5 years
Office Computers
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,124	2,586
Property and equipment, useful life in years	3 years
Computer and System Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,222	$ 1,193
Property and equipment, useful life in years	3 years