Schedule I - Condensed Statements of Operations (Parent Company Only) (Detail) - USD ($) $ 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
REVENUE
Total revenue									$ 2,666,958	$ 2,884,833	$ 2,697,829
OPERATING EXPENSES
Professional services									71,852	61,349	47,932
Other									43,951	89,486	44,069
Total 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
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
Parent Company [Member]
REVENUE
Equity in earnings of subsidiaries									153,450	392,574	145,008
Interest and other income									135,220	136,399	110,381
Total revenue									288,670	528,973	255,389
OPERATING EXPENSES
Professional services									2,017	1,719	1,692
Other									153	129	114
Total operating expenses									2,170	1,848	1,806
NET INCOME ATTRIBUTABLE TO LAZARD LTD									$ 286,500	$ 527,125	$ 253,583