Segment Information - Revenue and Operating Income (Loss), by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenue, Net of Reimbursements	$ 171,594	$ 160,071
Revenue
Reimbursements Revenue	4,680	4,587
Total revenue	176,274	164,658
Operating income (loss)
Operating (loss) income	16,391	13,121
Operating Segments [Member]
Operating income (loss)
Operating (loss) income	24,693	22,962
Global Operations Support [Member]
Operating income (loss)
Operating (loss) income	(8,302)	(9,841)
Executive Search [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net of Reimbursements	158,305	145,832
Operating income (loss)
Operating (loss) income	29,520	28,192
Heidrick Consulting [Domain] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net of Reimbursements	13,289	14,239
Operating income (loss)
Operating (loss) income	(4,827)	(5,230)
Executive Search and Leadership Consulting Americas Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net of Reimbursements	99,305	86,303
Operating income (loss)
Operating (loss) income	22,449	20,635
Executive Search and Leadership Consulting Europe Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net of Reimbursements	33,553	35,681
Operating income (loss)
Operating (loss) income	2,165	3,254
Executive Search and Leadership Consulting Asia Pacific Segment [Member] | Executive Search [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net of Reimbursements	25,447	23,848
Operating income (loss)
Operating (loss) income	$ 4,906	$ 4,303