Stockholders' Equity (Schedule Of Changes In Ownership Interests) (Details)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Beginning balance (in shares)	127,350,561	123,686,338
Common membership interest activity in connection with Equity compensation		3,000,000
Common membership interest activity in connection with Exchanges for Class A common stock
Common membership interest activity in connection with Business acquisitions	2,434,561	888,605
Repurchase of common membership interests from LAZ-MD Holdings	(19,032)	(167,286)
Ending balance (in shares)	129,766,090	127,407,657
LAZ-MD Holdings [Member]
Beginning balance (in shares)	7,652,625	31,520,426
Percentage Of Ownership, Beginning Balance	6.00%	25.50%
Common membership interest activity in connection with 2010 Secondary Offerings		(8,884,332)
Common membership interest activity in connection with Exchanges for Class A common stock	(738,655)	(11,665,618)
Repurchase of common membership interests from LAZ-MD Holdings	(19,032)	(167,286)
Ending balance (in shares)	6,894,938	10,803,190
Percentage Of Ownership, Ending Balance	5.30%	8.50%
Lazard Ltd [Member]
Beginning balance (in shares)	119,697,936	92,165,912
Percentage Of Ownership, Beginning Balance	94.00%	74.50%
Common membership interest activity in connection with Equity compensation		3,000,000
Common membership interest activity in connection with 2010 Secondary Offerings		8,884,332
Common membership interest activity in connection with Exchanges for Class A common stock	738,655	11,665,618
Common membership interest activity in connection with Business acquisitions	2,434,561	888,605
Repurchase of common membership interests from LAZ-MD Holdings
Ending balance (in shares)	122,871,152	116,604,467
Percentage Of Ownership, Ending Balance	94.70%	91.50%