Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total Cost	$ 60,671	$ 48,157
Less: Accumulated depreciation	(31,533)	(27,132)
Property and equipment, net of accumulated depreciation	29,138	21,025
Depreciation expense	5,600	5,300	$ 5,200
Computers and equipment
Property, Plant and Equipment [Line Items]
Total Cost	8,000	7,770
Computer software
Property, Plant and Equipment [Line Items]
Total Cost	4,554	4,372
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total Cost	10,566	8,658
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total Cost	$ 37,551	$ 27,357