Changes in Carrying Amounts of Goodwill by Operating Segment (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Goodwill, Gross		$ 1,392,437	$ 1,405,828	$ 1,412,872
Accumulated goodwill impairment		(194,139)	(194,139)	(194,139)
Goodwill, net		1,198,298	1,211,689	1,218,733
Acquisitions	[1]	70	6,926
Foreign currency translation adjustment and other		(13,461)	(13,970)
Corporate Finance / Restructuring
Goodwill [Line Items]
Goodwill, Gross		441,548	446,066	449,710
Goodwill, net		441,548	446,066	449,710
Acquisitions	[1]	70
Foreign currency translation adjustment and other		(4,588)	(3,644)
Forensic and Litigation Consulting
Goodwill [Line Items]
Goodwill, Gross		235,211	238,173	241,651
Goodwill, net		235,211	238,173	241,651
Acquisitions	[1]		(224)
Foreign currency translation adjustment and other		(2,962)	(3,254)
Economic Consulting
Goodwill [Line Items]
Goodwill, Gross		269,341	269,897	263,474
Goodwill, net		269,341	269,897	263,474
Acquisitions	[1]		7,150
Foreign currency translation adjustment and other		(556)	(727)
Technology
Goodwill [Line Items]
Goodwill, Gross		117,888	117,967	118,073
Goodwill, net		117,888	117,967	118,073
Foreign currency translation adjustment and other		(79)	(106)
Strategic Communications
Goodwill [Line Items]
Goodwill, Gross		328,449	333,725	339,964
Accumulated goodwill impairment		(194,139)	(194,139)	(194,139)
Goodwill, net		134,310	139,586	$ 145,825
Foreign currency translation adjustment and other		$ (5,276)	$ (6,239)

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