Property and Equipment, Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 12,353	$ 10,499
Less accumulated depreciation and amortization	(6,376)	(5,849)
Property and equipment, net	5,977	4,650
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,686	1,189
Property and equipment, useful life in years	5 years
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,763	2,776
Property and equipment, useful life in years	5 years
Systems Hardware
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,476	1,404
Property and equipment, useful life in years	5 years
Office Computers
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,019	3,745
Property and equipment, useful life in years	3 years
Computer and System Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,409	$ 1,385
Property and equipment, useful life in years	3 years