Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($)
Goodwill [Roll Forward]
Goodwill	$ 1,396,906
Accumulated goodwill impairment	(194,139)
Goodwill	1,202,767
Acquisitions	20,532
Foreign currency translation adjustment and other	465
Goodwill	1,417,903
Accumulated goodwill impairment	(194,139)
Goodwill	1,223,764
Corporate Finance & Restructuring
Goodwill [Roll Forward]
Goodwill	478,842
Goodwill	478,842
Acquisitions	20,532
Foreign currency translation adjustment and other	2,300
Goodwill	501,674
Goodwill	501,674
FLC
Goodwill [Roll Forward]
Goodwill	232,120
Goodwill	232,120
Foreign currency translation adjustment and other	(600)
Goodwill	231,520
Goodwill	231,520
Economic Consulting
Goodwill [Roll Forward]
Goodwill	268,677
Goodwill	268,677
Foreign currency translation adjustment and other	(7)
Goodwill	268,670
Goodwill	268,670
Technology
Goodwill [Roll Forward]
Goodwill	96,770
Goodwill	96,770
Foreign currency translation adjustment and other	(29)
Goodwill	96,741
Goodwill	96,741
Strategic Communications
Goodwill [Roll Forward]
Goodwill	320,497
Accumulated goodwill impairment	(194,139)
Goodwill	126,358
Foreign currency translation adjustment and other	(1,199)
Goodwill	319,298
Accumulated goodwill impairment	(194,139)
Goodwill	$ 125,159

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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