Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets
Allowance for bad debt	$ 1,003	$ 1,008
Accrued paid time off	1,624	2,592
Accrued bonus		55
Foreign net operating loss (NOL) carry forward	1,301	1,371
Federal/state net operating loss (NOL) carry forward	507	3,010
Stock option compensation	2,726	4,292
Deferred rent	3,355	5,423
Deferred compensation	3,238	3,662
Foreign tax credits	505	2,631
Foreign exchange	2,051	5,349
Accrued liabilities and other	3,272	3,378
Deferred Tax Assets, gross, before valuation allowance	21,367	34,780
Less: Valuation Allowance	(1,636)	(1,131)	$ (933)	$ (542)
Total Deferred Tax Assets	19,731	33,649
Deferred Tax Liabilities
Retention	(1,375)	(1,684)
Prepaid expenses	(1,045)	(1,654)
Payroll taxes	(489)	(617)
Unbilled revenue	(5,407)	(8,728)
Depreciation	(4,773)	(6,664)
Amortization	(39,993)	(51,842)
Deferred gain and other		(1,574)
Total Deferred Tax Liabilities	(53,082)	(72,763)
Total Net Deferred Tax Liability	(33,351)	(39,114)
State and Local Jurisdiction
Deferred Tax Assets
Tax credits	$ 1,785	1,784
United States Government
Deferred Tax Assets
Tax credits		$ 225