Changes in Carrying Amounts of Goodwill by Operating Segment (Detail) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2016	Dec. 31, 2015
Goodwill [Line Items]
Foreign currency translation adjustment and other	$ (10,068)
Goodwill, Gross	1,382,369	$ 1,392,437
Accumulated goodwill impairment	(194,139)	(194,139)
Goodwill, net	1,188,230	1,198,298
Corporate Finance & Restructuring
Goodwill [Line Items]
Foreign currency translation adjustment and other	1,203
Goodwill, Gross	442,751	441,548
Goodwill, net	442,751	441,548
Forensic and Litigation Consulting
Goodwill [Line Items]
Foreign currency translation adjustment and other	(2,850)
Goodwill, Gross	232,361	235,211
Goodwill, net	232,361	235,211
Economic Consulting
Goodwill [Line Items]
Foreign currency translation adjustment and other	(700)
Goodwill, Gross	268,641	269,341
Goodwill, net	268,641	269,341
Technology
Goodwill [Line Items]
Foreign currency translation adjustment and other	(202)
Goodwill, Gross	117,686	117,888
Goodwill, net	117,686	117,888
Strategic Communications
Goodwill [Line Items]
Foreign currency translation adjustment and other	(7,519)
Goodwill, Gross	320,930	328,449
Accumulated goodwill impairment	(194,139)	(194,139)
Goodwill, net	$ 126,791	$ 134,310

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

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