Business Segments - Revenue by Category (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 128,782	$ 106,144	$ 243,333	$ 234,425
Automotive
Segment Reporting Information [Line Items]
Revenue	34,870	23,178	61,629	56,599
Financial Services
Segment Reporting Information [Line Items]
Revenue	21,039	17,698	40,637	38,156
Defense & Aerospace
Segment Reporting Information [Line Items]
Revenue	19,034	19,417	37,694	40,920
Technology
Segment Reporting Information [Line Items]
Revenue	9,676	8,069	18,283	16,120
All Other
Segment Reporting Information [Line Items]
Revenue	44,163	37,782	85,090	82,630
Organizational Performance Solutions
Segment Reporting Information [Line Items]
Revenue	42,103	36,407	82,575	78,454
Technical Performance Solutions
Segment Reporting Information [Line Items]
Revenue	55,259	48,967	106,679	106,284
Automotive Performance Solutions
Segment Reporting Information [Line Items]
Revenue	31,420	20,770	54,079	49,687
North America
Segment Reporting Information [Line Items]
Revenue	82,999	72,913	155,328	157,849
North America | Automotive
Segment Reporting Information [Line Items]
Revenue	26,927	17,210	46,606	42,173
North America | Financial Services
Segment Reporting Information [Line Items]
Revenue	10,031	9,399	19,337	19,091
North America | Defense & Aerospace
Segment Reporting Information [Line Items]
Revenue	18,261	18,154	35,782	38,003
North America | Technology
Segment Reporting Information [Line Items]
Revenue	8,135	7,150	15,057	14,136
North America | All Other
Segment Reporting Information [Line Items]
Revenue	19,645	21,000	38,546	44,446
North America | Organizational Performance Solutions
Segment Reporting Information [Line Items]
Revenue	23,482	22,493	46,138	46,493
North America | Technical Performance Solutions
Segment Reporting Information [Line Items]
Revenue	35,412	35,199	68,614	75,096
North America | Automotive Performance Solutions
Segment Reporting Information [Line Items]
Revenue	24,105	15,221	40,576	36,260
EMEA
Segment Reporting Information [Line Items]
Revenue	31,831	23,680	61,804	55,578
EMEA | Automotive
Segment Reporting Information [Line Items]
Revenue	1,672	1,495	3,201	4,125
EMEA | Financial Services
Segment Reporting Information [Line Items]
Revenue	6,524	5,283	13,008	12,685
EMEA | Defense & Aerospace
Segment Reporting Information [Line Items]
Revenue	773	1,263	1,912	2,917
EMEA | Technology
Segment Reporting Information [Line Items]
Revenue	1,379	567	2,893	1,345
EMEA | All Other
Segment Reporting Information [Line Items]
Revenue	21,483	15,072	40,790	34,506
EMEA | Organizational Performance Solutions
Segment Reporting Information [Line Items]
Revenue	10,867	9,171	21,556	22,106
EMEA | Technical Performance Solutions
Segment Reporting Information [Line Items]
Revenue	19,579	13,661	37,608	30,966
EMEA | Automotive Performance Solutions
Segment Reporting Information [Line Items]
Revenue	1,385	848	2,640	2,506
Emerging Markets
Segment Reporting Information [Line Items]
Revenue	13,952	9,551	26,201	20,998
Emerging Markets | Automotive
Segment Reporting Information [Line Items]
Revenue	6,271	4,473	11,822	10,301
Emerging Markets | Financial Services
Segment Reporting Information [Line Items]
Revenue	4,484	3,016	8,292	6,380
Emerging Markets | Defense & Aerospace
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Emerging Markets | Technology
Segment Reporting Information [Line Items]
Revenue	162	352	333	639
Emerging Markets | All Other
Segment Reporting Information [Line Items]
Revenue	3,035	1,710	5,754	3,678
Emerging Markets | Organizational Performance Solutions
Segment Reporting Information [Line Items]
Revenue	7,754	4,743	14,881	9,855
Emerging Markets | Technical Performance Solutions
Segment Reporting Information [Line Items]
Revenue	268	107	457	222
Emerging Markets | Automotive Performance Solutions
Segment Reporting Information [Line Items]
Revenue	$ 5,930	$ 4,701	$ 10,863	$ 10,921