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
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to Lazard Ltd - basic	$ 159,692	$ 107,553
Net income attributable to Lazard Ltd - diluted	$ 159,692	$ 107,553
Weighted average number of shares of Class A common stock outstanding	119,695,749	122,531,221
Add - adjustment for shares of Class A common stock issuable on a non-contingent basis	234,357	283,942
Weighted average number of shares of Class A common stock outstanding - basic	119,930,106	122,815,163
Weighted average number of incremental shares of Class A common stock issuable from share-based incentive compensation	12,212,288	9,874,212
Weighted average number of shares of Class A common stock outstanding - diluted	132,142,394	132,689,375
Net income attributable to Lazard Ltd per share of Class A common stock:
Basic	$ 1.33	$ 0.88
Diluted	$ 1.21	$ 0.81