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 ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income attributable to Lazard Ltd - basic									$ 253,583	$ 387,698	$ 986,373
Net income attributable to Lazard Ltd - diluted									$ 253,583	$ 387,698	$ 986,373
Weighted average number of shares of Class A common stock outstanding									121,309,174	124,635,160	125,294,261
Add - adjustment for shares of Class A common stock issuable on a non-contingent basis									264,268	135,241	72,011
Weighted average number of shares of Class A common stock outstanding - basic									121,573,442	124,770,401	125,366,272
Weighted average number of incremental shares of Class A common stock issuable from share-based incentive compensation									10,906,286	7,863,229	7,878,274
Weighted average number of shares of Class A common stock outstanding - diluted									132,479,728	132,633,630	133,244,546
Net income attributable to Lazard Ltd per share of Class A common stock:
Basic	$ (0.70)	$ 0.90	$ 0.98	$ 0.88	$ 1.04	$ 0.90	$ 0.64	$ 0.53	$ 2.09	$ 3.11	$ 7.87
Diluted	$ (0.70)	$ 0.82	$ 0.91	$ 0.81	$ 0.96	$ 0.85	$ 0.61	$ 0.50	$ 1.91	$ 2.92	$ 7.40