Segment Information - Identifiable Assets, Goodwill and Other Intangible Assets, Net, by Segment (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current assets
Total allocated current assets	$ 472,686,000	$ 494,482,000
Unallocated non-current assets	222,354,000	220,925,000
Intangible Assets, Net (Including Goodwill)	92,772,000	128,766,000
Goodwill and other intangible assets, net
Assets	787,812,000	844,173,000
Payments to Acquire Property, Plant, and Equipment	7,322,000	3,352,000	$ 5,960,000
Executive Search [Member]
Current assets
Total allocated current assets	446,201,000	462,015,000
Operating Segments [Member]
Current assets
Total allocated current assets	470,747,000	492,643,000
Corporate Segment [Member]
Current assets
Total allocated current assets	1,939,000	1,839,000
Executive Search Member [Member]
Current assets
Intangible Assets, Net (Including Goodwill)	92,772,000	128,766,000
Heidrick Consulting [Member]
Current assets
Total allocated current assets	24,546,000	30,628,000
Intangible Assets, Net (Including Goodwill)	0	0
Americas [Member] | Executive Search [Member]
Current assets
Total allocated current assets	284,837,000	286,818,000
Americas [Member] | Executive Search Member [Member]
Current assets
Intangible Assets, Net (Including Goodwill)	91,868,000	93,054,000
Europe [Member] | Executive Search [Member]
Current assets
Total allocated current assets	84,841,000	96,230,000
Europe [Member] | Executive Search Member [Member]
Current assets
Intangible Assets, Net (Including Goodwill)	852,000	26,893,000
Asia Pacific [Member] | Executive Search [Member]
Current assets
Total allocated current assets	76,523,000	78,967,000
Asia Pacific [Member] | Executive Search Member [Member]
Current assets
Intangible Assets, Net (Including Goodwill)	$ 52,000	$ 8,819,000