Incentive Plans - Schedule of Activity Relating to RSUs and DSUs (Parenthetical) (Detail) - shares	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Dividend participation rights	739,079	841,433

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