Stockholders' Equity - Net Income (Loss) Attributable to Noncontrolling Interests (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests	$ 1,259	$ 372	$ 3,341	$ 3,504	$ (3,330)	$ 4,434	$ 9,562	$ 4,976	$ 8,476	$ 15,642	$ 19,444
Noncontrolling interests	81,884				140,713				81,884	140,713
LAZ-MD Holdings [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests									5,114	11,964	12,564
Noncontrolling interests	5,405				31,954				5,405	31,954
Edgewater [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests									3,491	4,130	6,690
Noncontrolling interests	75,262				91,713				75,262	91,713
Other [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests									(129)	(452)	190
Noncontrolling interests	$ 1,217				$ 17,046				$ 1,217	$ 17,046