Goodwill and Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($)	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Goodwill beginning of period	$ 1,227,593,000
Foreign currency translation adjustment and other	(1,237,000)
Intersegment transfers in/(out)	0
Goodwill end of period	1,226,356,000
Corporate Finance & Restructuring
Goodwill [Roll Forward]
Goodwill beginning of period	516,500,000
Foreign currency translation adjustment and other	(2,523,000)
Intersegment transfers in/(out)	23,086,000
Goodwill end of period	537,063,000
Accumulated impairment loss	0	$ 0
Forensic and Litigation Consulting
Goodwill [Roll Forward]
Goodwill beginning of period	234,872,000
Foreign currency translation adjustment and other	309,000
Intersegment transfers in/(out)	(23,086,000)
Goodwill end of period	212,095,000
Accumulated impairment loss	0	0
Economic Consulting
Goodwill [Roll Forward]
Goodwill beginning of period	268,055,000
Foreign currency translation adjustment and other	44,000
Intersegment transfers in/(out)	0
Goodwill end of period	268,099,000
Accumulated impairment loss	0	0
Technology
Goodwill [Roll Forward]
Goodwill beginning of period	96,727,000
Foreign currency translation adjustment and other	18,000
Intersegment transfers in/(out)	0
Goodwill end of period	96,745,000
Accumulated impairment loss	0	0
Strategic Communications
Goodwill [Roll Forward]
Goodwill beginning of period	111,439,000
Foreign currency translation adjustment and other	915,000
Intersegment transfers in/(out)	0
Goodwill end of period	112,354,000
Accumulated impairment loss	194,100,000	194,100,000
Goodwill	$ 306,500,000	$ 305,600,000