Stockholders' Equity (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended				6 Months Ended				1 Months Ended	6 Months Ended	65 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	3 Months Ended	6 Months Ended					6 Months Ended
	Mar. 31, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2011 Share Repurchase Program [Member]	Feb. 28, 2011 Share Repurchase Program [Member]	Dec. 31, 2010 Share Repurchase Program [Member]	Jan. 31, 2010 Share Repurchase Program [Member]	Mar. 31, 2010 Class A Common Stock Shares Received Upon Exchange [Member]	Jun. 30, 2011 Lazard Group Common Membership Interests [Member]	Jun. 30, 2011 Lazard Group Common Membership Interests [Member]	Mar. 31, 2010 Estate of Former Chairman and Chief Executive Officer [Member]	Jul. 27, 2011 Class A Common Stock	Mar. 31, 2010 Class A Common Stock	Mar. 31, 2010 Class A Common Stock	Jun. 30, 2011 Class A Common Stock	Jun. 30, 2011 Series A Preferred Stock	Dec. 31, 2010 Series A Preferred Stock	Jun. 30, 2011 Series B Preferred Stock	Dec. 31, 2010 Series B Preferred Stock	Jun. 30, 2011 Subsidiaries Of Lazard Ltd [Member]	Jun. 30, 2011 LAZ-MD Holdings [Member]	Jun. 30, 2011 Lazard Ltd [Member]	Jun. 30, 2010 Lazard Ltd [Member]
Tax Distributions by Subsidiary to controlling and noncontrolling common membership interests				$ 0																				$ 0	$ 0
Quarterly dividend declared per share		$ 0.16	$ 0.125	$ 0.285	$ 0.25											$ 0.16
Newly issued common stock																		3,000,000
Shares authorized pertaining to share based compensation arrangements, 2005 Plan																	25,000,000	25,000,000	25,000,000
Secondary offering - shares sold			0		0												7,869,311
Secondary offering - price of shares sold															$ 35.90
Secondary offering - shares sold pertaining to shares previously received												7,262
Secondary offering - shares sold pertaining to shares received upon simultaneous exchange												6,180,639
Secondary offering - shares sold pertaining to shares received upon simultaneous exchange pertaining to shares held by Estate of Chairman and CEO															5,958,000
Secondary offering - shares sold pertaining to shares held by Estate	1,681,410
Stock/membership interest repurchase program authorized amount								450,000	250,000		200,000
Shares in exchange of a like number of common membership interests																										728,385	11,465,108
Share repurchase amount unused								165,740
Number of shares/common membership interests purchased													19,032	1,400,089					3,156,416
Aggregate cost of shares/common membership interests purchased													$ 794						$ 126,237
Average price per share/common membership interest														$ 32.66
Common stock of parent held by subsidiary								4,339,875		6,847,508
Authorized shares of preferred stock		15,000,000		15,000,000		15,000,000	15,000,000
Par value of preferred stock		$ 0.01		$ 0.01		$ 0.01	$ 0.01
Outstanding shares of preferred stock																				22,021	22,021	0	0
Convertible preferred stock																				4,862	4,862
Remaining outstanding preferred shares																				17,159	17,159
Initial conversion rate																				100	100
Percentage of common membership interests and corresponding voting interests in subsidiary by non controlling interests		5.40%		5.40%		6.00%