Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment	$ 154,193	$ 129,286
Less -- accumulated depreciation	96,197	72,344
Total	57,996	56,942
Computer and related equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	115,444	96,138
Furniture, fixtures and equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	17,556	14,956
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	16,628	12,670
Work-in-progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	$ 4,565	$ 5,522