Incentive Plans - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Lazard Fund Interests [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, years	1 year
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	$ 211,254
Unrecognized compensation expense, years	1 year
DSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual compensation paid in DSUs	31,280	38,771
Units granted under the directors deferred unit plan	7,035	4,467
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 42,545
Unrecognized compensation expense, years	10 months 24 days
PRSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 13,089
Unrecognized compensation expense, years	10 months 24 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 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.
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	1,267,560	1,382,153
Delivery of common stock associated with stock awards	2,670,410	2,851,741
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	135,528	129,389
Delivery of common stock associated with stock awards	323,286	600,068
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	126,264	64,169
Delivery of common stock associated with stock awards	699,301	352,849
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	30.00%
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

Delivery of common stock associated with stock awards.

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

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

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

+ References

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- Definition

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

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

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

+ References

No definition available.

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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

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Section 50
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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- 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
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- 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
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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
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- 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.

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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).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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- 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

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