Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 123,576	$ 113,938
Less: accumulated depreciation	(85,510)	(79,233)
Total	38,066	34,705
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	109,885	100,392
Furniture, equipment and building improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 13,691	$ 13,546