Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Thousands	9 Months Ended
Sep. 30, 2019 USD ($)
Goodwill [Roll Forward]
Goodwill	$ 1,366,455
Accumulated goodwill impairment	(194,139)
Goodwill	1,172,316
Acquisitions	30,807
Foreign currency translation adjustment and other	(5,717)
Goodwill	1,391,545
Accumulated goodwill impairment	(194,139)
Goodwill	1,197,406
Corporate Finance & Restructuring
Goodwill [Roll Forward]
Goodwill	450,997
Goodwill	450,997
Foreign currency translation adjustment and other	(1,740)
Goodwill	480,064
Goodwill	480,064
Forensic and Litigation Consulting
Goodwill [Roll Forward]
Goodwill	231,537
Goodwill	231,537
Foreign currency translation adjustment and other	(1,228)
Goodwill	230,309
Goodwill	230,309
Economic Consulting
Goodwill [Roll Forward]
Goodwill	268,547
Goodwill	268,547
Foreign currency translation adjustment and other	(270)
Goodwill	268,277
Goodwill	268,277
Technology
Goodwill [Roll Forward]
Goodwill	96,723
Goodwill	96,723
Foreign currency translation adjustment and other	(45)
Goodwill	96,678
Goodwill	96,678
Strategic Communications
Goodwill [Roll Forward]
Goodwill	318,651
Accumulated goodwill impairment	(194,139)
Goodwill	124,512
Acquisitions	0
Foreign currency translation adjustment and other	(2,434)
Goodwill	316,217
Accumulated goodwill impairment	(194,139)
Goodwill	$ 122,078

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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