Property and Equipment - Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 116,610	$ 114,560
Accumulated depreciation and amortization	(78,558)	(74,076)
Total property and equipment, net	38,052	40,484
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	18,873	17,847
Software and Software Development Costs
Property Plant And Equipment [Line Items]
Property and equipment, gross	42,835	41,269
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	26,076	26,570
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 28,826	$ 28,874