Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of property and equipment
Property and equipment, at cost	$ 208,484	$ 205,413
Accumulated depreciation	(106,035)	(99,979)
Property and equipment, net	102,449	105,434
Depreciation	18,359	16,046	$ 14,634
Leasehold improvements
Summary of property and equipment
Property and equipment, at cost	$ 22,426	21,741
Leasehold improvements | Minimum
Summary of property and equipment
Estimated useful lives	1 year
Leasehold improvements | Maximum
Summary of property and equipment
Estimated useful lives	15 years
Furniture and fixtures
Summary of property and equipment
Property and equipment, at cost	$ 30,501	29,462
Furniture and fixtures | Minimum
Summary of property and equipment
Estimated useful lives	3 years
Furniture and fixtures | Maximum
Summary of property and equipment
Estimated useful lives	10 years
Equipment
Summary of property and equipment
Property and equipment, at cost	$ 20,616	20,901
Equipment | Minimum
Summary of property and equipment
Estimated useful lives	2 years
Equipment | Maximum
Summary of property and equipment
Estimated useful lives	26 years
Computer software
Summary of property and equipment
Property and equipment, at cost	$ 100,941	96,310
Computer software | Minimum
Summary of property and equipment
Estimated useful lives	1 year
Computer software | Maximum
Summary of property and equipment
Estimated useful lives	10 years
Data processing equipment
Summary of property and equipment
Property and equipment, at cost	$ 19,458	20,335
Data processing equipment | Minimum
Summary of property and equipment
Estimated useful lives	1 year
Data processing equipment | Maximum
Summary of property and equipment
Estimated useful lives	5 years
Buildings
Summary of property and equipment
Property and equipment, at cost	$ 11,699	12,860
Buildings | Minimum
Summary of property and equipment
Estimated useful lives	1 year
Buildings | Maximum
Summary of property and equipment
Estimated useful lives	30 years
Land
Summary of property and equipment
Property and equipment, at cost	$ 2,843	3,804
Property and equipment under capital leases
Summary of property and equipment
Property and equipment, at cost	1,800	2,100
Accumulated depreciation	$ (800)	$ (1,100)