Revenue - Revenue by Category (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 515,160	$ 509,208	$ 490,559
Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	116,077	111,387	109,299
Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	100,116	103,057	102,894
Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	49,211	52,929	45,760
Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	41,840	36,624	38,838
U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	38,366	34,729	35,202
UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	18,733	27,734	25,487
Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,593	28,613	27,352
Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	29,672	28,691	22,451
Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	15,927	17,518	24,074
Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,759	17,797	17,546
Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	57,866	50,129	41,656
Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	206,388	207,007	204,007
Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	110,426	101,252	101,908
Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	103,740	101,196	101,939
Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	94,606	99,753	82,705
Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	379,745	373,680	363,120
Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	129,935	130,757	119,877
Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	33,322	30,204	30,623
Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(27,842)	(25,433)	(23,061)
Workforce Excellence [Member]
Disaggregation of Revenue [Line Items]
Revenue	316,814	308,259	305,915
Workforce Excellence [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	10,646	10,102	7,672
Workforce Excellence [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	87,813	86,718	87,102
Workforce Excellence [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	33,055	35,795	37,135
Workforce Excellence [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	37,088	34,195	35,580
Workforce Excellence [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	29,584	25,254	25,011
Workforce Excellence [Member] | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	18,733	27,734	25,487
Workforce Excellence [Member] | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	14,083	18,123	19,410
Workforce Excellence [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	25,989	22,142	21,262
Workforce Excellence [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	15,070	16,449	23,253
Workforce Excellence [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	15,009	8,420	7,113
Workforce Excellence [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	29,744	23,327	16,890
Workforce Excellence [Member] | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	206,388	207,007	204,007
Workforce Excellence [Member] | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	110,426	101,252	101,908
Workforce Excellence [Member] | Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0
Workforce Excellence [Member] | Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0
Workforce Excellence [Member] | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	213,938	198,653	198,393
Workforce Excellence [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	91,764	100,296	97,274
Workforce Excellence [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	30,688	29,828	30,173
Workforce Excellence [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(19,576)	(20,518)	(19,925)
Business Transformation Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	198,346	200,949	184,644
Business Transformation Services [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	105,431	101,285	101,627
Business Transformation Services [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	12,303	16,339	15,792
Business Transformation Services [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	16,156	17,134	8,625
Business Transformation Services [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,752	2,429	3,258
Business Transformation Services [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,782	9,475	10,191
Business Transformation Services [Member] | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0
Business Transformation Services [Member] | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,510	10,490	7,942
Business Transformation Services [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,683	6,549	1,189
Business Transformation Services [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	857	1,069	821
Business Transformation Services [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,750	9,377	10,433
Business Transformation Services [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	28,122	26,802	24,766
Business Transformation Services [Member] | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0
Business Transformation Services [Member] | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0
Business Transformation Services [Member] | Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	103,740	101,196	101,939
Business Transformation Services [Member] | Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	94,606	99,753	82,705
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	165,807	175,027	164,727
Business Transformation Services [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	38,171	30,461	22,603
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,634	376	450
Business Transformation Services [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ (8,266)	$ (4,915)	$ (3,136)