Incentive Plans - Schedule of Issuance of RSUs and Charges to Retained Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of RSUs issued	535,695	613,795
Charges to retained earnings, net of estimated forfeitures	$ 28,406	$ 25,977

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