Incentive Plans - Schedule of Issuance of RSUs and Charges to Retained Earnings (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of RSUs issued	529,616	203,537
Charges to retained earnings, net of estimated forfeitures	$ 26,461	$ 9,387

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