Segment Information - Revenue and Operating Income (Loss), by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
CEO Restricted Stock (2014 Grants), Outstanding	100.00%		100.00%
Goodwill and Intangible Asset Impairment	$ 0	$ 0	$ 39,158	$ 0
Revenue:
Revenue before reimbursements (net revenue)	159,800	143,519	452,020	422,569
Reimbursements	4,665	4,720	13,740	13,773
Total revenue	164,465	148,239	465,760	436,342
Operating income (loss):
Operating (loss) income	14,022	12,006	(7,751)	27,568
Operating Segments [Member]
Operating income (loss):
Operating (loss) income	27,898	22,993	31,265	62,497
Global Operations Support [Member]
Operating income (loss):
Operating (loss) income	(13,876)	(10,987)	(39,016)	(34,929)
Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	144,113	126,259	403,138	372,696
Operating income (loss):
Operating (loss) income	28,918	23,961	77,352	70,339
Leadership Consulting [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	8,771	8,635	29,970	23,203
Operating income (loss):
Operating (loss) income	(1,162)	(1,009)	(3,732)	(5,914)
Culture Shaping [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	6,916	8,625	18,912	26,670
Operating income (loss):
Operating (loss) income	142	41	(42,355)	(1,928)
Executive Search and Leadership Consulting Americas Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	88,254	75,602	248,442	230,486
Operating income (loss):
Operating (loss) income	23,574	19,208	66,086	58,583
Executive Search and Leadership Consulting Europe Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	33,994	27,844	90,534	78,783
Operating income (loss):
Operating (loss) income	4,131	2,530	5,947	6,926
Executive Search and Leadership Consulting Asia Pacific Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	21,865	22,813	64,162	63,427
Operating income (loss):
Operating (loss) income	$ 1,213	$ 2,223	$ 5,319	$ 4,830