Organization And Basis Of Presentation - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012 Segment	Sep. 30, 2012 Class B Common Stock	Dec. 31, 2011 Class B Common Stock	Sep. 30, 2012 Class A Common Stock [Member]	Dec. 31, 2011 Class A Common Stock [Member]	Sep. 30, 2011 Class A Common Stock [Member]	Sep. 30, 2012 LAZ-MD Holdings LLC [Member]	Dec. 31, 2011 LAZ-MD Holdings LLC [Member]	Sep. 30, 2012 LAZ-MD Holdings LLC [Member] Class B Common Stock	Dec. 31, 2011 LAZ-MD Holdings LLC [Member] Class B Common Stock	Sep. 30, 2012 Lazard Ltd [Member]	Dec. 31, 2011 Lazard Ltd [Member]
Organization And Basis Of Presentation [Line Items]
Common membership interests held							94.90%	94.80%			5.10%	5.20%
Governing Operating Agreement, Date	May 10, 2005
Common membership voting power held									5.10%	5.20%
Common stock, par value		$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock, shares outstanding		1	1						1
Common stock, shares issued		1	1	123,201,012	123,009,311	3,682,116			1
Number of business segments	2