Incentive Plans - Schedule of Activity Relating to RSUs and DSUs (Parenthetical) (Detail) - shares	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Dividend participation rights	636,207	739,079

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