Segment Information - Reconciliation of Adjusted EBITDA from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Revenue before reimbursements (net revenue)	$ 283,578	$ 265,197
Reimbursements	3,864	3,901
Total revenue	287,442	269,098
Salary and benefits	172,632	160,949
General and administrative	30,284	31,345
Cost of services	30,059	27,432
Adjusted EBITDA	29,122	25,868
Operating Segments
Segment Reporting Information [Line Items]
Total segment operating expenses	232,975	219,726
Adjusted EBITDA	50,603	45,471
Operating Segments \| On-Demand Talent
Segment Reporting Information [Line Items]
Revenue before reimbursements (net revenue)	42,564	37,857
Salary and benefits	11,598	11,593
General and administrative	3,741	3,095
Cost of services	26,825	24,090
Total segment operating expenses	42,164	38,778
Adjusted EBITDA	400	(921)
Operating Segments \| Heidrick Consulting
Segment Reporting Information [Line Items]
Revenue before reimbursements (net revenue)	27,624	25,859
Salary and benefits	21,635	18,884
General and administrative	4,851	5,660
Cost of services	3,234	3,342
Total segment operating expenses	29,720	27,886
Adjusted EBITDA	(2,096)	(2,027)
Operating Segments \| Americas \| Executive Search
Segment Reporting Information [Line Items]
Revenue before reimbursements (net revenue)	144,404	136,679
Salary and benefits	90,093	84,026
General and administrative	10,089	10,782
Cost of services	0	0
Total segment operating expenses	100,182	94,808
Adjusted EBITDA	44,222	41,871
Operating Segments \| Europe \| Executive Search
Segment Reporting Information [Line Items]
Revenue before reimbursements (net revenue)	45,391	41,481
Salary and benefits	32,489	30,254
General and administrative	7,860	7,874
Cost of services	0	0
Total segment operating expenses	40,349	38,128
Adjusted EBITDA	5,042	3,353
Operating Segments \| Asia Pacific \| Executive Search
Segment Reporting Information [Line Items]
Revenue before reimbursements (net revenue)	23,595	23,321
Salary and benefits	16,817	16,192
General and administrative	3,743	3,934
Cost of services	0	0
Total segment operating expenses	20,560	20,126
Adjusted EBITDA	3,035	3,195
Research and development
Segment Reporting Information [Line Items]
Adjusted EBITDA	4,624	4,925
Research and development \| On-Demand Talent
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Research and development \| Heidrick Consulting
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Research and development \| Americas \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Research and development \| Europe \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Research and development \| Asia Pacific \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Global Operations Support
Segment Reporting Information [Line Items]
Adjusted EBITDA	16,857	14,678
Global Operations Support \| On-Demand Talent
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Global Operations Support \| Heidrick Consulting
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Global Operations Support \| Americas \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Global Operations Support \| Europe \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Global Operations Support \| Asia Pacific \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Total reconciling expenses
Segment Reporting Information [Line Items]
Adjusted EBITDA	21,481	19,603
Total reconciling expenses \| On-Demand Talent
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Total reconciling expenses \| Heidrick Consulting
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Total reconciling expenses \| Americas \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Total reconciling expenses \| Europe \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	0	0
Total reconciling expenses \| Asia Pacific \| Executive Search
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 0	$ 0

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