Goodwill and Intangible Assets - Summary of Changes in Carrying Amounts of Goodwill by Operating Segment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill beginning of period	$ 1,234,879,000	$ 1,202,767,000
Acquisitions	5,493,000	20,632,000
Foreign currency translation adjustment and other	(7,581,000)	11,480,000
Goodwill end of period	1,232,791,000	1,234,879,000
Corporate Finance
Goodwill [Roll Forward]
Goodwill beginning of period	506,072,000	478,842,000
Acquisitions	0	20,632,000
Foreign currency translation adjustment and other	(5,026,000)	6,598,000
Goodwill end of period	501,046,000	506,072,000
Accumulated impairment loss	0	0	$ 0
FLC
Goodwill [Roll Forward]
Goodwill beginning of period	233,374,000	232,120,000
Acquisitions	5,493,000	0
Foreign currency translation adjustment and other	(938,000)	1,254,000
Goodwill end of period	237,929,000	233,374,000
Accumulated impairment loss	0	0	0
Economic Consulting
Goodwill [Roll Forward]
Goodwill beginning of period	269,087,000	268,677,000
Acquisitions	0	0
Foreign currency translation adjustment and other	(229,000)	410,000
Goodwill end of period	268,858,000	269,087,000
Accumulated impairment loss	0	0	0
Technology
Goodwill [Roll Forward]
Goodwill beginning of period	96,821,000	96,770,000
Acquisitions	0	0
Foreign currency translation adjustment and other	(10,000)	51,000
Goodwill end of period	96,811,000	96,821,000
Accumulated impairment loss	0	0	0
Strategic Communications
Goodwill [Roll Forward]
Goodwill beginning of period	129,525,000	126,358,000
Acquisitions	0	0
Foreign currency translation adjustment and other	(1,378,000)	3,167,000
Goodwill end of period	128,147,000	129,525,000
Accumulated impairment loss	194,100,000	194,100,000	194,100,000
Goodwill, gross	$ 322,300,000	$ 323,700,000	$ 320,500,000