Segment Reporting (Details) - USD ($)	3 Months Ended		9 Months Ended		21 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 263,825,000	$ 143,544,000	$ 717,462,000	$ 460,628,000
Revenues	265,315,000	144,501,000	721,281,000	467,183,000
Operating Income (Loss) [Abstract]
Operating Income (Loss)	33,342,000	(38,233,000)	81,656,000	(44,067,000)
Restructuring Charges	3,262,000	(48,115,000)	(3,792,000)	(48,115,000)	$ (56,163,000)
Reimbursements
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	1,490,000	957,000	3,819,000	6,555,000
Americas
Operating Income (Loss) [Abstract]
Restructuring Charges	2,900,000		(3,900,000)	(27,600,000)
Europe
Operating Income (Loss) [Abstract]
Goodwill, Impairment Loss		24,500,000		24,500,000
Restructuring Charges	0.1	9,600,000	(100,000)	9,600,000
Asia Pacific
Operating Income (Loss) [Abstract]
Goodwill, Impairment Loss		8,500,000		8,500,000
Restructuring Charges		4,600,000	(100,000)	4,600,000
Heidrick Consulting
Operating Income (Loss) [Abstract]
Restructuring Charges	300,000	(4,500,000)	(400,000)	(4,500,000)
On-Demand Talent
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	24.3		43
Operating Income (Loss) [Abstract]
Operating Income (Loss)	0.9		1
Operating Segments
Operating Income (Loss) [Abstract]
Operating Income (Loss)	46,804,000	(25,802,000)	116,514,000	(14,226,000)
Operating Segments | Executive Search Member
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	221,646,000	129,243,000	625,397,000	418,850,000
Operating Income (Loss) [Abstract]
Operating Income (Loss)	48,479,000	(16,516,000)	126,377,000	7,473,000
Operating Segments | Executive Search Member | Americas
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	148,844,000	79,947,000	412,740,000	265,088,000
Operating Income (Loss) [Abstract]
Operating Income (Loss)	38,972,000	(7,934,000)	99,822,000	40,900,000
Restructuring Charges	2,887,000		(3,882,000)		(34,359,000)
Operating Segments | Executive Search Member | Europe
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	42,676,000	28,902,000	125,228,000	92,108,000
Operating Income (Loss) [Abstract]
Operating Income (Loss)	4,795,000	(6,856,000)	13,314,000	(26,874,000)
Restructuring Charges	(9,000)		97,000		(8,507,000)
Operating Segments | Executive Search Member | Asia Pacific
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	30,126,000	20,394,000	87,429,000	61,654,000
Operating Income (Loss) [Abstract]
Operating Income (Loss)	4,712,000	(1,726,000)	13,241,000	(6,553,000)
Restructuring Charges	0		124,000		(4,490,000)
Operating Segments | Heidrick Consulting
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	17,892,000	14,301,000	49,059,000	41,778,000
Operating Income (Loss) [Abstract]
Operating Income (Loss)	(2,556,000)	(9,286,000)	(10,897,000)	(21,699,000)
Restructuring Charges	279,000		(355,000)		(5,013,000)
Operating Segments | On-Demand Talent
Revenues [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	24,287,000		43,006,000
Operating Income (Loss) [Abstract]
Operating Income (Loss)	881,000		1,034,000
Corporate, Non-Segment
Operating Income (Loss) [Abstract]
Operating Income (Loss)	(13,462,000)	(12,431,000)	(34,858,000)	(29,841,000)
Restructuring Charges	$ 105,000	$ (1,900,000)	$ 224,000	$ (1,900,000)	$ (3,794,000)