Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets
Allowance for bad debt	$ 888	$ 1,321
Accrued paid time off	1,671	1,437
Foreign net operating loss (NOL) carry forward	866	1,144
State net operating loss (NOL) carry forward	714	507
Stock option compensation	2,666	2,332
Deferred rent	3,129	3,127
Deferred compensation	3,902	3,348
Foreign tax credits	4,508	3,968
Foreign exchange	3,579	2,430
Foreign deferred	200	342
Accrued liabilities and other	5,318	4,079
Deferred Tax Assets, gross, before valuation allowance	29,467	26,076
Less: Valuation Allowance	(5,374)	(5,112)	$ (1,636)	$ (1,131)
Total Deferred Tax Assets	24,093	20,964
Deferred Tax Liabilities
Retention	(1,395)	(1,239)
Prepaid expenses	(1,451)	(1,301)
Payroll taxes	(593)	(495)
Unbilled revenue	(2,691)	(4,135)
Depreciation	(3,112)	(7,306)
Amortization	(52,076)	(46,051)
Deferred gain and other	(396)	(602)
Total Deferred Tax Liabilities	(61,714)	(61,129)
Total Net Deferred Tax Liability	(37,621)	(40,165)
State and Local Jurisdiction
Deferred Tax Assets
Tax credits	$ 2,026	$ 2,041