Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Goodwill [Line Items]
Goodwill	$ 1,366,455
Accumulated goodwill impairment	(194,139)
Goodwill	1,172,316
Foreign currency translation adjustment and other	2,426
Goodwill	1,368,881
Accumulated goodwill impairment	(194,139)
Goodwill	1,174,742
Corporate Finance & Restructuring
Goodwill [Line Items]
Goodwill	450,997
Goodwill	450,997
Foreign currency translation adjustment and other	244
Goodwill	451,241
Goodwill	451,241
Forensic and Litigation Consulting
Goodwill [Line Items]
Goodwill	231,537
Goodwill	231,537
Foreign currency translation adjustment and other	447
Goodwill	231,984
Goodwill	231,984
Economic Consulting
Goodwill [Line Items]
Goodwill	268,547
Goodwill	268,547
Foreign currency translation adjustment and other	95
Goodwill	268,642
Goodwill	268,642
Technology
Goodwill [Line Items]
Goodwill	96,723
Goodwill	96,723
Foreign currency translation adjustment and other	37
Goodwill	96,760
Goodwill	96,760
Strategic Communications
Goodwill [Line Items]
Goodwill	318,651
Accumulated goodwill impairment	(194,139)
Goodwill	124,512
Foreign currency translation adjustment and other	1,603
Goodwill	320,254
Accumulated goodwill impairment	(194,139)
Goodwill	$ 126,115

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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