Segment Information - Revenue, Operating Income, Depreciation and Amortization, and Capital Expenditures, by Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Revenue before reimbursements (net revenue)	$ 621,400	$ 582,390	$ 531,139
Reimbursements	18,656	18,516	17,172
Total revenue	640,056	600,906	548,311
Operating Income (Loss)
Operating (loss) income	(26,523)	35,233	34,062
Depreciation and Amortization
Depreciation and amortization	14,774	16,433	13,696
Capital Expenditures
Capital expenditures	15,686	8,382	15,863
Operating Segments [Member]
Operating Income (Loss)
Operating (loss) income	28,265	82,454	80,662
Depreciation and Amortization
Depreciation and amortization	13,333	14,986	11,684
Capital Expenditures
Capital expenditures	12,388	7,061	9,679
Corporate, Non-Segment [Member]
Operating Income (Loss)
Global Operations Support (6)	54,788	47,221	46,600
Depreciation and Amortization
Depreciation and amortization	1,441	1,447	2,012
Capital Expenditures
Capital expenditures	3,298	1,321	6,184
Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	552,044	507,365	475,767
Operating Income (Loss)
Operating (loss) income	85,697	85,507	77,596
Depreciation and Amortization
Depreciation and amortization	9,447	8,144	6,771
Capital Expenditures
Capital expenditures	11,216	6,402	9,254
Leadership Consulting [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	41,227	38,806	19,045
Operating Income (Loss)
Operating (loss) income	(15,614)	(1,495)	(1,847)
Depreciation and Amortization
Depreciation and amortization	2,240	2,501	393
Capital Expenditures
Capital expenditures	470	380	330
Culture Shaping [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	28,129	36,219	36,327
Operating Income (Loss)
Operating (loss) income	(41,818)	(1,558)	4,913
Depreciation and Amortization
Depreciation and amortization	1,646	4,341	4,520
Capital Expenditures
Capital expenditures	702	279	95
Executive Search and Leadership Consulting Americas Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	339,793	313,292	294,606
Operating Income (Loss)
Operating (loss) income	81,531	73,857	68,043
Depreciation and Amortization
Depreciation and amortization	4,661	3,892	3,858
Capital Expenditures
Capital expenditures	7,123	2,221	7,334
Executive Search and Leadership Consulting Europe Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	125,346	108,754	92,135
Operating Income (Loss)
Operating (loss) income	2,038	6,851	3,644
Depreciation and Amortization
Depreciation and amortization	3,207	2,478	1,530
Capital Expenditures
Capital expenditures	1,460	835	890
Executive Search and Leadership Consulting Asia Pacific Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Revenue:
Revenue before reimbursements (net revenue)	86,905	85,319	89,026
Operating Income (Loss)
Operating (loss) income	2,128	4,799	5,909
Depreciation and Amortization
Depreciation and amortization	1,579	1,774	1,383
Capital Expenditures
Capital expenditures	$ 2,633	$ 3,346	$ 1,030