Fair Value Measurements - Fair Value of Certain Investments Based on NAV (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Unfunded commitments to private equity investments	$ 7,518	$ 10,613

Unfunded commitments to private equity investments consolidated but not owned for fair value investments that calculate net asset value.

No definition available.

Name:	laz_UnfundedCommitmentsToPrivateEquityInvestmentsConsolidatedButNotOwnedForFairValueInvestmentsThatCalculateNetAssetValue
Namespace Prefix:	laz_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant