Consolidated VIEs - Summary of Consolidated VIE Assets and Liabilities (Parenthetical) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Investments	$ 535,848	$ 575,148
Lazard Fund Interests [Member] \| Lazard Group LLC [Member]
Variable Interest Entity [Line Items]
Investments	$ 79,791

Sum of the carrying amounts as of the balance sheet date of all investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(h))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Name:	us-gaap_Investments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant