Revenue - Revenue by Category (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 123,566	$ 124,097	$ 382,289	$ 377,705
Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,269	25,176	81,748	83,142
Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	25,056	27,512	76,532	76,504
Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	11,292	12,302	37,227	38,732
Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	10,301	8,922	31,087	28,171
U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,775	8,572	27,446	25,438
UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,456	6,858	14,889	21,789
Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,645	6,294	17,980	20,733
Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,865	7,260	24,027	20,777
Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,960	4,166	11,749	12,981
Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,824	4,095	16,886	13,083
Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	15,123	12,940	42,718	36,355
Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	51,387	52,524	156,244	152,713
Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	29,129	24,498	82,800	75,523
Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	19,944	22,768	73,566	75,756
Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,106	24,307	69,679	73,713
Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	91,444	89,023	279,749	278,990
Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	30,059	32,723	96,656	93,932
Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,314	8,331	24,703	22,660
Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(6,251)	(5,980)	(18,819)	(17,877)
Workforce Excellence [Member]
Disaggregation of Revenue [Line Items]
Revenue	80,516	77,022	239,044	228,236
Workforce Excellence [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,738	2,399	8,614	7,175
Workforce Excellence [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	22,364	23,583	67,522	64,066
Workforce Excellence [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,558	8,874	25,621	26,762
Workforce Excellence [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,113	8,457	27,769	26,275
Workforce Excellence [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,673	6,220	20,704	18,528
Workforce Excellence [Member] | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,456	6,858	14,889	21,789
Workforce Excellence [Member] | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,315	3,785	11,027	12,785
Workforce Excellence [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,705	5,582	21,619	16,003
Workforce Excellence [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,719	4,016	11,228	12,371
Workforce Excellence [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,892	1,822	9,743	5,912
Workforce Excellence [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,983	5,426	20,308	16,570
Workforce Excellence [Member] | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	51,387	52,524	156,244	152,713
Workforce Excellence [Member] | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	29,129	24,498	82,800	75,523
Workforce Excellence [Member] | Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Workforce Excellence [Member] | Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Workforce Excellence [Member] | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	56,064	48,382	158,935	147,423
Workforce Excellence [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	21,153	25,540	69,248	73,078
Workforce Excellence [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,205	8,255	24,405	22,328
Workforce Excellence [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(4,906)	(5,155)	(13,544)	(14,593)
Business Transformation Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	43,050	47,075	143,245	149,469
Business Transformation Services [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	20,531	22,777	73,134	75,967
Business Transformation Services [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,692	3,929	9,010	12,438
Business Transformation Services [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,734	3,428	11,606	11,970
Business Transformation Services [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,188	465	3,318	1,896
Business Transformation Services [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,102	2,352	6,742	6,910
Business Transformation Services [Member] | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Business Transformation Services [Member] | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,330	2,509	6,953	7,948
Business Transformation Services [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,160	1,678	2,408	4,774
Business Transformation Services [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	241	150	521	610
Business Transformation Services [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,932	2,273	7,143	7,171
Business Transformation Services [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,140	7,514	22,410	19,785
Business Transformation Services [Member] | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Business Transformation Services [Member] | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Business Transformation Services [Member] | Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	19,944	22,768	73,566	75,756
Business Transformation Services [Member] | Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,106	24,307	69,679	73,713
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	35,380	40,641	120,814	131,567
Business Transformation Services [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,906	7,183	27,408	20,854
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	109	76	298	332
Business Transformation Services [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ (1,345)	$ (825)	$ (5,275)	$ (3,284)