Number of shares of equity interests issued or issuable to acquire entity.

Name:	laz_BusinessAcquisitionEquityInterestIssuedOrIssuableNumberOfShares
Namespace Prefix:	laz
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of acquisition cost of a business combination allocated to other liabilities of the acquired entity.

+ Details

Name:	laz_BusinessAcquisitionPurchasePriceAllocationOtherLiabilities
Namespace Prefix:	laz
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Merger Transaction

+ Details

Name:	laz_MergerTransactionAbstract
Namespace Prefix:	laz
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cash paid to acquire the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 68
-Subparagraph f(1)

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 51
-Subparagraph d

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of acquisition cost of a business combination allocated to accrued expenses of the acquired entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 51
-Subparagraph e

+ Details

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationCurrentLiabilitiesAccruedLiabilities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Lam Merger Transaction (Details) (USD $) In Thousands, except Share data	Oct. 31, 2011	Jun. 30, 2011	Dec. 31, 2010	Jan. 02, 2009
Lam Merger Transaction
Cash payment made for merger related cost	$ 90,300			$ 60,100
Business acquisition, equity interest issued or issuable, number of shares	2,201,457
Accrued compensation and benefits		15,473	15,152
Other liabilities		$ 73,752	$ 71,394