Deferred incentive compensation awards granted.

No definition available.

Name:	laz_DeferredIncentiveCompensationAwardsGranted
Namespace Prefix:	laz_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Delivery of common stock associated with stock awards.

+ References

No definition available.

+ Details

Name:	laz_DeliveryOfCommonStockAssociatedWithStockAwards
Namespace Prefix:	laz_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of annual compensation received by directors in deferred stock units.

+ References

No definition available.

+ Details

Name:	laz_PercentageOfAnnualCompensationReceivedByDirectorsInDeferredStockUnits
Namespace Prefix:	laz_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of outstanding shares available under an equity-based compensation award plan.

+ References

No definition available.

+ Details

Name:	laz_PercentageOfOutstandingSharesAvailableUnderAnEquityBasedCompensationAwardPlan
Namespace Prefix:	laz_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of target number of shares subject to each PRSU no longer subject to forfeiture due to threshold level of performance being achieved.

+ References

No definition available.

+ Details

Name:	laz_PercentageOfTargetNumberOfSharesSubjectToEachPrsuNoLongerSubjectToForfeitureDueToThresholdLevelOfPerformanceBeingAchieved
Namespace Prefix:	laz_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award award vesting terms.

+ References

No definition available.

+ Details

Name:	laz_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingTerms
Namespace Prefix:	laz_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award target shares earned description.

+ References

No definition available.

+ Details

Name:	laz_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetSharesEarnedDescription
Namespace Prefix:	laz_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment awards vesting date.

+ References

No definition available.

+ Details

Name:	laz_ShareBasedCompensationArrangementByShareBasedPaymentAwardsVestingDate
Namespace Prefix:	laz_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares granted to directors under the Directors Fee deferral unit plan.

+ References

No definition available.

+ Details

Name:	laz_UnitsGrantedDirectorsDeferredUnitPlan
Namespace Prefix:	laz_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Describe the conversion features of common stock if such stock is convertible. That is, shares of common stock into which another convertible security was converted, or shares of common stock into which another class of common stock was converted.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockConversionBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares issued pursuant to the terms of a deferred compensation arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the equity-based award expires, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=laz_LazardFundInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=laz_OneThirdVestingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=laz_TwoThirdVestingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TitleOfIndividualAxis=laz_NonExecutiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=laz_DeferredStockUnitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=laz_PerformanceBasedRestrictedStockUnitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=laz_AwardedUnderTwoThousandEightPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=laz_TwoThousandAndFivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Incentive Plans - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 26, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, years	2 years 8 months 12 days
Deferred incentive compensation awards including PRSUs valued at target payout level	$ 351,000
Lazard Fund Interests [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, years		10 months 24 days
Lazard Fund Interests [Member] \| Subsequent Event [Member] \| One-Third Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards, vesting date	Mar. 02, 2020
Lazard Fund Interests [Member] \| Subsequent Event [Member] \| Two-Thirds Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards, vesting date	Mar. 01, 2021
Non-Executive [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of annual compensation received by directors in the form of DSUs		55.00%
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock conversion basis		one-for-one
Grant date fair value, amortized periods		generally one-third after two years, and the remaining two-thirds after the third year
Unrecognized compensation expense		$ 139,793
Unrecognized compensation expense, years		9 months 18 days
RSUs [Member] \| Subsequent Event [Member] \| One-Third Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards, vesting date	Mar. 02, 2020
RSUs [Member] \| Subsequent Event [Member] \| Two-Thirds Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards, vesting date	Mar. 01, 2021
DSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual compensation paid in DSUs		31,280	38,771	23,961
Units granted under the directors deferred unit plan		13,882	10,043	2,482
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense		$ 27,181
Unrecognized compensation expense, years		9 months 18 days
PRSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense		$ 9,174
Unrecognized compensation expense, years		8 months 12 days
Percentage of target number of shares subject to each PRSU no longer subject to forfeiture due to threshold level of performance being achieved		25.00%
Descriptions of vesting period associated with PRSUs		PRSUs will vest on a single date approximately three years following the date of the grant
Vesting period of PRSUs granted		3 years
PSRU's target share distribution for Class A common stock, description		The target number of shares of Class A common stock subject to each PRSU is one; however, based on the achievement of the performance criteria, the number of shares of Class A common stock that may be received in connection with each PRSU generally can range from zero to two times the target number.
PRSUs [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards, vesting date	Mar. 01, 2021
Class A Common Stock [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Withholding taxes in lieu of share delivery		1,290,601	1,421,396	2,249,935
Delivery of common stock associated with stock awards		2,707,562	3,118,998	5,506,133
Class A Common Stock [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Withholding taxes in lieu of share delivery		150,470	141,026	108,833
Delivery of common stock associated with stock awards		341,206	678,846	438,291
Class A Common Stock [Member] \| Restricted Stock [Member] \| Subsequent Event [Member] \| One-Third Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards, vesting date	Mar. 02, 2020
Class A Common Stock [Member] \| Restricted Stock [Member] \| Subsequent Event [Member] \| Two-Thirds Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards, vesting date	Mar. 01, 2021
Class A Common Stock [Member] \| PRSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Withholding taxes in lieu of share delivery		127,530	64,169	32,086
Delivery of common stock associated with stock awards		698,035	352,852	664,413
Class A Common Stock [Member] \| Awarded Under 2008 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of outstanding class A common stock that can be awarded under plan		30.00%
Compensation plan expiration period		May 31, 2018
Class A Common Stock [Member] \| 2005 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized pertaining to share based compensation arrangements, 2005 Plan		25,000,000