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, 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
Selected Quarterly Financial Information [Abstract]
Net Revenue	$ 678,808	$ 624,859	$ 717,180	$ 623,464	$ 691,565	$ 608,908	$ 534,680	$ 498,218	$ 2,644,311	$ 2,333,371	$ 2,353,608
Operating expenses	320,272	480,647	544,679	473,267	534,709	459,916	421,444	399,841	1,818,865	1,815,910	2,370,228
Operating Income (Loss)	358,536	144,212	172,501	150,197	156,856	148,992	113,236	98,377	825,446	517,461	(16,620)
NET INCOME	(82,954)	111,470	120,901	110,430	128,987	112,618	81,364	70,723	259,847	393,692	992,932
Net Income Attributable to Noncontrolling Interests	604	2,260	523	2,877	1,005	82	1,007	3,900	6,264	5,994	6,559
Net income (loss) attributable to Lazard Ltd	$ (83,558)	$ 109,210	$ 120,378	$ 107,553	$ 127,982	$ 112,536	$ 80,357	$ 66,823	$ 253,583	$ 387,698	$ 986,373
NET INCOME PER SHARE OF 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
DIVIDENDS DECLARED PER SHARE OF COMMON STOCK	$ 0.41	$ 0.41	$ 0.41	$ 1.58	$ 0.38	$ 0.38	$ 0.38	$ 1.55	$ 2.81	$ 2.69	$ 2.35