Goodwill and Other Intangible Assets - Summary of Other Intangible Assets Net by Segment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Net Carrying Amount	$ 2,158	$ 20,690
Executive Search [Member]
Finite-Lived Intangible Assets [Line Items]
Net Carrying Amount	2,158	3,565
Executive Search [Member] | Americas [Member]
Finite-Lived Intangible Assets [Line Items]
Net Carrying Amount	252	501
Executive Search [Member] | Europe [Member]
Finite-Lived Intangible Assets [Line Items]
Net Carrying Amount	1,799	2,937
Executive Search [Member] | Asia Pacific [Member]
Finite-Lived Intangible Assets [Line Items]
Net Carrying Amount	107	127
Leadership Consulting [Member]
Finite-Lived Intangible Assets [Line Items]
Net Carrying Amount	0	6,223
Culture Shaping [Member]
Finite-Lived Intangible Assets [Line Items]
Net Carrying Amount	$ 0	$ 10,902