Incentive Plans - Schedule of Issuance of RSUs and Charges to Retained Earnings (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of RSUs issued	636,207	739,079
Charges to retained earnings, net of estimated forfeitures	$ 33,627	$ 31,335

Charge to retained earnings pertaining to issuance of restricted stock units in connection with participation rights.

No definition available.

Name:	laz_ChargeToRetainedEarningsPertainingToIssuanceOfRestrictedStockUnitsInConnectionWithParticipationRights
Namespace Prefix:	laz_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration