Revenue - Revenue by Category (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 106,144	$ 149,413	$ 234,425	$ 288,886
Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,375	45,760	55,530	83,534
Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	17,941	22,170	38,568	43,291
Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,105	14,190	20,221	28,478
Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,956	10,306	14,404	22,864
U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	12,135	11,851	24,923	23,375
UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,182	4,369	9,449	8,412
Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,361	6,075	10,105	11,840
Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,855	7,974	17,168	15,587
Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,297	4,433	5,137	8,809
Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,822	6,620	13,144	13,447
Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	11,115	15,665	25,776	29,249
Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	38,326	44,789	80,824	89,431
Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	27,485	39,114	59,365	75,950
Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,368	42,113	55,856	77,664
Organizational Development
Disaggregation of Revenue [Line Items]
Revenue	16,965	23,397	38,380	45,841
Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	78,999	110,773	172,411	211,057
Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	26,864	34,905	60,697	69,200
Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	9,404	15,389	19,588	26,665
Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(9,123)	(11,654)	(18,271)	(18,036)
Workforce Excellence
Disaggregation of Revenue [Line Items]
Revenue	65,811	83,903	140,189	165,381
Workforce Excellence | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,180	3,668	3,633	7,266
Workforce Excellence | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	16,027	19,931	35,183	39,137
Workforce Excellence | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,858	9,610	15,016	18,880
Workforce Excellence | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,078	8,850	12,353	20,380
Workforce Excellence | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	10,698	10,060	21,904	19,855
Workforce Excellence | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Workforce Excellence | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,795	5,563	8,910	10,869
Workforce Excellence | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,141	4,684	14,437	12,194
Workforce Excellence | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,084	3,994	4,707	8,124
Workforce Excellence | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,830	5,083	10,938	9,977
Workforce Excellence | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,120	12,460	13,108	18,699
Workforce Excellence | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	38,326	44,789	80,824	89,431
Workforce Excellence | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	27,485	39,114	59,365	75,950
Workforce Excellence | Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Workforce Excellence | Organizational Development
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Workforce Excellence | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	51,781	64,468	108,344	124,132
Workforce Excellence | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	14,413	18,643	32,085	37,921
Workforce Excellence | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,586	8,693	11,031	14,835
Workforce Excellence | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(5,969)	(7,901)	(11,271)	(11,507)
Business Transformation Services
Disaggregation of Revenue [Line Items]
Revenue	40,333	65,510	94,236	123,505
Business Transformation Services | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	22,195	42,092	51,897	76,268
Business Transformation Services | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,914	2,239	3,385	4,154
Business Transformation Services | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,247	4,580	5,205	9,598
Business Transformation Services | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	878	1,456	2,051	2,484
Business Transformation Services | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,437	1,791	3,019	3,520
Business Transformation Services | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,182	4,369	9,449	8,412
Business Transformation Services | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	566	512	1,195	971
Business Transformation Services | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,714	3,290	2,731	3,393
Business Transformation Services | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	213	439	430	685
Business Transformation Services | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	992	1,537	2,206	3,470
Business Transformation Services | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,995	3,205	12,668	10,550
Business Transformation Services | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Business Transformation Services | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Business Transformation Services | Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,368	42,113	55,856	77,664
Business Transformation Services | Organizational Development
Disaggregation of Revenue [Line Items]
Revenue	16,965	23,397	38,380	45,841
Business Transformation Services | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	27,218	46,305	64,067	86,925
Business Transformation Services | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	12,451	16,262	28,612	31,279
Business Transformation Services | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,818	6,696	8,557	11,830
Business Transformation Services | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ (3,154)	$ (3,753)	$ (7,000)	$ (6,529)