Supplemental Financial Information - Quarterly Results - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Net Revenue	$ 721,341	$ 591,068	$ 630,690	$ 643,674	$ 687,235	$ 626,481	$ 757,938	$ 754,698	$ 2,586,773	$ 2,826,352	$ 2,644,311
Operating expenses	602,364	538,695	529,005	524,011	530,918	487,800	557,998	568,870	2,194,075	2,145,586	1,818,865
Operating Income (Loss)	118,977	52,373	101,685	119,663	156,317	138,681	199,940	185,828	392,698	680,766	825,446
NET INCOME	79,531	48,196	73,513	96,476	113,684	108,725	148,379	161,661	297,716	532,449	259,847
Net income (loss) attributable to noncontrolling interests	2,554	1,492	7,736	(566)	288	1,651	1,416	1,969	11,216	5,324	6,264
Net income attributable to Lazard Ltd	$ 76,977	$ 46,704	$ 65,777	$ 97,042	$ 113,396	$ 107,074	$ 146,963	$ 159,692	$ 286,500	$ 527,125	$ 253,583
NET INCOME PER SHARE OF COMMON STOCK:
Basic	$ 0.70	$ 0.42	$ 0.57	$ 0.87	$ 0.97	$ 0.90	$ 1.22	$ 1.33	$ 2.57	$ 4.43	$ 2.09
Diluted	0.67	0.40	0.55	0.80	0.89	0.82	1.13	1.21	2.44	4.06	1.91
Dividend declared per share of common stock	$ 0.47	$ 0.47	$ 0.47	$ 0.94	$ 0.44	$ 0.44	$ 0.44	$ 1.71	$ 2.35	$ 3.03	$ 2.81