Revenue - Revenue by Category (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 133,691	$ 131,161	$ 258,723	$ 253,608
Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	31,294	30,851	58,478	57,966
Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	26,302	24,937	51,475	48,982
Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	12,640	13,895	25,928	26,431
Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	11,654	9,212	20,771	19,249
U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,829	8,170	17,669	16,866
UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,947	8,202	10,433	14,932
Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,661	7,739	12,335	14,441
Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,804	6,964	16,163	13,516
Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,056	4,056	7,790	8,814
Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	5,505	4,770	10,062	8,989
Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	13,999	12,365	27,619	23,422
Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	50,418	49,213	99,320	94,542
Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	29,838	26,819	55,367	53,033
Sales Enablement [Member]
Disaggregation of Revenue [Line Items]
Revenue	27,799	28,371	51,649	52,988
Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	25,636	26,758	52,387	53,045
Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	98,683	98,629	188,305	189,967
Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	33,143	31,865	66,597	61,209
Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,606	7,088	16,389	14,330
Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(6,741)	(6,421)	(12,568)	(11,898)
Workforce Excellence [Member]
Disaggregation of Revenue [Line Items]
Revenue	80,256	76,032	154,687	147,575
Workforce Excellence [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,818	2,411	5,656	4,669
Workforce Excellence [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	22,010	20,017	43,113	38,603
Workforce Excellence [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,662	8,978	17,341	17,253
Workforce Excellence [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	10,701	8,657	18,343	17,707
Workforce Excellence [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,468	5,802	12,922	11,955
Workforce Excellence [Member] | UK Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,947	8,202	10,433	14,932
Workforce Excellence [Member] | Information and Communication Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,811	4,033	7,110	8,013
Workforce Excellence [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,834	5,307	14,432	10,346
Workforce Excellence [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,822	3,961	7,505	8,324
Workforce Excellence [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,903	2,273	4,752	3,997
Workforce Excellence [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	7,280	6,391	13,080	11,776
Workforce Excellence [Member] | Managed Learning Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	50,418	49,213	99,320	94,542
Workforce Excellence [Member] | Engineering and Technical Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	29,838	26,819	55,367	53,033
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	51,509	47,718	96,949	92,658
Workforce Excellence [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	24,605	26,019	49,562	49,610
Workforce Excellence [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,489	6,943	16,200	14,073
Workforce Excellence [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	(4,347)	(4,648)	(8,024)	(8,766)
Business Transformation Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	53,435	55,129	104,036	106,033
Business Transformation Services [Member] | Automotive Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	28,476	28,440	52,822	53,297
Business Transformation Services [Member] | Financial and Insurance Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	4,292	4,920	8,362	10,379
Business Transformation Services [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,978	4,917	8,587	9,178
Business Transformation Services [Member] | Energy, Oil and Gas Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	953	555	2,428	1,542
Business Transformation Services [Member] | U.S. Government Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,361	2,368	4,747	4,911
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	2,850	3,706	5,225	6,428
Business Transformation Services [Member] | Aerospace Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	970	1,657	1,731	3,170
Business Transformation Services [Member] | Electronics Semiconductor Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	234	95	285	490
Business Transformation Services [Member] | Life Sciences Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,602	2,497	5,310	4,992
Business Transformation Services [Member] | Other Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenue	6,719	5,974	14,539	11,646
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	27,799	28,371	51,649	52,988
Business Transformation Services [Member] | Organizational Development [Member]
Disaggregation of Revenue [Line Items]
Revenue	25,636	26,758	52,387	53,045
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Americas [Member]
Disaggregation of Revenue [Line Items]
Revenue	47,174	50,911	91,356	97,309
Business Transformation Services [Member] | Reportable Geographical Components [Member] | EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,538	5,846	17,035	11,599
Business Transformation Services [Member] | Reportable Geographical Components [Member] | Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenue	117	145	189	257
Business Transformation Services [Member] | Geography Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ (2,394)	$ (1,773)	$ (4,544)	$ (3,132)