Recent Accounting Developments - Additional Information (Detail) $ in Thousands	6 Months Ended
Jun. 30, 2020 USD ($)
Adjustments for New Accounting Principle, Early Adoption [Member]
Cumulative-effect adjustment to retained ernings related to fee receivables recorded from adoption of new guidance	$ 7,575

Represents the quantification of the effect of adopting the new accounting standard or change in accounting principle expected by the entity to have a significant effect on the entity's financial statements.

No definition available.

Name:	laz_NewAccountingPronouncementOrChangeInAccountingPrincipleEffectOfAdoptionQuantification1
Namespace Prefix:	laz_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration