Summary of Changes in Carrying Amounts of Goodwill by Operating Segment (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Goodwill, Gross		$ 1,374,140	$ 1,392,437	$ 1,405,828
Accumulated goodwill impairment		(194,139)	(194,139)	(194,139)
Goodwill, net		1,180,001	1,198,298	1,211,689
Acquisitions	[1]	218	70
Foreign currency translation adjustment and other		(18,515)	(13,461)
Corporate Finance & Restructuring
Goodwill [Line Items]
Goodwill, Gross		440,666	441,548	446,066
Goodwill, net		440,666	441,548	446,066
Acquisitions	[1]		70
Foreign currency translation adjustment and other		(882)	(4,588)
Forensic and Litigation Consulting
Goodwill [Line Items]
Goodwill, Gross		230,544	235,211	238,173
Goodwill, net		230,544	235,211	238,173
Foreign currency translation adjustment and other		(4,667)	(2,962)
Economic Consulting
Goodwill [Line Items]
Goodwill, Gross		268,209	269,341	269,897
Goodwill, net		268,209	269,341	269,897
Foreign currency translation adjustment and other		(1,132)	(556)
Technology
Goodwill [Line Items]
Goodwill, Gross		117,607	117,888	117,967
Goodwill, net		117,607	117,888	117,967
Foreign currency translation adjustment and other		(281)	(79)
Strategic Communications
Goodwill [Line Items]
Goodwill, Gross		317,114	328,449	333,725
Accumulated goodwill impairment		(194,139)	(194,139)	(194,139)
Goodwill, net		122,975	134,310	$ 139,586
Acquisitions	[1]	218
Foreign currency translation adjustment and other		$ (11,553)	$ (5,276)

[1] Includes adjustments during the purchase price allocation period.