Net Income Attributable to Noncontrolling Interests (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable To Noncontrolling Interests	$ 372	$ 4,434	$ 7,217	$ 18,972
Noncontrolling interests	119,999		119,999		140,713
LAZ-MD Holdings [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable To Noncontrolling Interests	1,937	4,209	4,956	11,955
Noncontrolling interests	35,819		35,819		31,954
Edgewater [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable To Noncontrolling Interests	(1,704)	587	2,168	7,492
Noncontrolling interests	82,669		82,669		91,713
Other Noncontrolling Interests [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable To Noncontrolling Interests	139	(362)	93	(475)
Noncontrolling interests	$ 1,511		$ 1,511		$ 17,046