Incentive Plans - Schedule of Activity Relating to RSUs and DSUs (Parenthetical) (Detail) - shares	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Dividend participation rights	746,324	866,914

Issuance of restricted stock units in connection with dividend participation rights.

No definition available.

Name:	laz_IssuanceOfRestrictedStockUnitsInConnectionWithDividendParticipationRights
Namespace Prefix:	laz_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration