Schedule of Issuance of RSUs And Charges to Retained Earnings (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of RSUs issued	479,958	251,146
Charges to retained earnings, net of estimated forfeitures	$ 11,770	$ 8,169

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