Property and Equipment - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, net	$ 17,424	$ 14,091	$ 13,985
Depreciation expense	5,882	$ 4,087	$ 3,333
Leasehold improvements paid for by landlord
Property, Plant and Equipment [Line Items]
Property and equipment, net	$ 1,000