Schedule I - Condensed Statements of Operations (Parent Company Only) (Detail) - USD ($) $ 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
REVENUE
Total revenue									$ 2,697,829	$ 2,383,663	$ 2,404,767
OPERATING EXPENSES
Professional services									47,932	45,512	49,529
Other									44,069	41,219	99,142
Total 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
NET INCOME 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
Parent Company [Member]
REVENUE
Equity in earnings of subsidiaries									145,008	326,366	931,036
Interest and other income									110,381	63,019	57,258
Total revenue									255,389	389,385	988,294
OPERATING EXPENSES
Professional services									1,692	1,580	1,779
Other									114	107	142
Total operating expenses									1,806	1,687	1,921
NET INCOME ATTRIBUTABLE TO LAZARD LTD									$ 253,583	$ 387,698	$ 986,373