Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 13,368	$ 10,499
Less accumulated depreciation and amortization		(7,339)	(5,849)
Property and equipment, net		6,029	4,650
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 1,734	1,189
Property and equipment, useful life in years		5 years
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	[1]	$ 4,025	2,776
Property and equipment, useful life in years	[1]	5 years
Systems Hardware
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 1,471	1,404
Property and equipment, useful life in years		5 years
Office Computers
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 4,667	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		$ 1,471	$ 1,385
Property and equipment, useful life in years		3 years

[1] Lesser of the lease term or the estimated useful lives of the improvements, which may be up to 5 years.