Net Income Per Share of Class A Common Stock - Company's Basic and Diluted Net Income Per Share and Weighted Average Shares Outstanding (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income attributable to Lazard Ltd	$ 172,384	$ 88,859	$ 85,192	$ 80,842	$ 53,217	$ 60,282	$ 31,353	$ 15,360	$ 427,277	$ 160,212	$ 84,309
Add (deduct) - adjustment associated with Class A common stock issuable on a non-contingent basis											7
Net income attributable to Lazard Ltd - basic									427,277	160,212	84,316
Adjustments to income relating to interest expense and changes in net income attributable to noncontrolling interests resulting from assumed Class A common stock issuances in connection with share-based incentive compensation, and exchangeable interests, net of tax									581	1,065	371
Net income attributable to Lazard Ltd - diluted									$ 427,858	$ 161,277	$ 84,687
Weighted average number of shares of Class A common stock outstanding									121,942,939	120,096,305	116,163,821
Add - adjustment for shares of Class A common stock issuable on a non-contingent basis									408,897	757,962	790,168
Weighted average number of shares of Class A common stock outstanding - basic									122,351,836	120,854,267	116,953,989
Weighted average number of incremental shares of Class A common stock issuable from share-based incentive compensation and exchangeable interests									11,461,287	12,882,812	12,371,633
Weighted average number of shares of Class A common stock outstanding - diluted									133,813,123	133,737,079	129,325,622
Net income attributable to Lazard Ltd per share of Class A common stock:
Basic	$ 1.41	$ 0.73	$ 0.69	$ 0.66	$ 0.44	$ 0.49	$ 0.26	$ 0.13	$ 3.49	$ 1.33	$ 0.72
Diluted	$ 1.29	$ 0.67	$ 0.64	$ 0.61	$ 0.40	$ 0.45	$ 0.24	$ 0.12	$ 3.20	$ 1.21	$ 0.65