Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 128,617	$ 113,938
Less: accumulated depreciation	(88,829)	(79,233)
Total	39,788	34,705
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	113,463	100,392
Furniture, equipment and building improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 15,154	$ 13,546