Revenue - Revenue by Category (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price	$ 400	$ 300	$ 1,300	$ 1,300
Revenue	139,005	123,566	427,891	382,289
Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	34,497	23,269	118,031	81,748
Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	27,340	25,056	70,631	76,532
Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	13,946	11,292	42,424	37,227
Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,398	10,301	32,262	31,087
U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	11,284	9,775	34,659	27,446
UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,654	4,456	13,066	14,889
Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,870	5,645	16,710	17,980
Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,961	7,865	25,548	24,027
Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,618	3,960	12,427	11,749
Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,412	6,824	19,859	16,886
Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	13,025	15,123	42,274	42,718
Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	55,901	51,387	159,972	156,244
Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	26,589	29,129	83,027	82,800
Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	33,826	19,944	115,754	71,593
Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	22,689	23,106	69,138	71,652
Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	102,094	91,444	313,534	279,749
Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	34,281	30,059	103,098	97,661
Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	14,311	8,314	40,976	23,698
Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(11,681)	(6,251)	(29,717)	(18,819)
Workforce Excellence [Member]
Disaggregation of Revenue [Line Items]
Revenue	82,490	80,516	242,999	239,044
Workforce Excellence [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,354	2,738	6,176	8,614
Workforce Excellence [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	24,450	22,364	62,847	67,522
Workforce Excellence [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,001	7,558	25,395	25,621
Workforce Excellence [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,910	9,113	27,972	27,769
Workforce Excellence [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,282	7,673	28,768	20,704
Workforce Excellence [Member] | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,654	4,456	13,066	14,889
Workforce Excellence [Member] | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,909	3,315	10,372	11,027
Workforce Excellence [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,644	6,705	22,198	21,619
Workforce Excellence [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,229	3,719	11,444	11,228
Workforce Excellence [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,091	4,892	14,799	9,743
Workforce Excellence [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,966	7,983	19,962	20,308
Workforce Excellence [Member] | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	55,901	51,387	159,972	156,244
Workforce Excellence [Member] | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	26,589	29,129	83,027	82,800
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	58,469	56,064	170,953	158,935
Workforce Excellence [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	21,721	21,153	66,418	70,253
Workforce Excellence [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,558	8,205	24,393	23,400
Workforce Excellence [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(7,258)	(4,906)	(18,765)	(13,544)
Business Transformation Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	56,515	43,050	184,892	143,245
Business Transformation Services [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	32,143	20,531	111,855	73,134
Business Transformation Services [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,890	2,692	7,784	9,010
Business Transformation Services [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,945	3,734	17,029	11,606
Business Transformation Services [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,488	1,188	4,290	3,318
Business Transformation Services [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,002	2,102	5,891	6,742
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	1,961	2,330	6,338	6,953
Business Transformation Services [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,317	1,160	3,350	2,408
Business Transformation Services [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	389	241	983	521
Business Transformation Services [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,321	1,932	5,060	7,143
Business Transformation Services [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,059	7,140	22,312	22,410
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	33,826	19,944	115,754	71,593
Business Transformation Services [Member] | Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	22,689	23,106	69,138	71,652
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	43,625	35,380	142,581	120,814
Business Transformation Services [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	12,560	8,906	36,680	27,408
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,753	109	16,583	298
Business Transformation Services [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ (4,423)	$ (1,345)	$ (10,952)	$ (5,275)