Incentive Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Apr. 29, 2021	Apr. 24, 2018	Sep. 30, 2022	Sep. 30, 2021
Lazard Fund Interests [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, years			10 months 24 days
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
Number of dividend participation rights issued			336,740
Charges to retained earnings, net of estimated forfeitures			$ 11,416
Weighted-average grant date fair value of awards granted			$ 33.64	$ 43.19
Unrecognized compensation expense			$ 142,667
Unrecognized compensation expense, years			1 year
DSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of awards granted			$ 35.53	46.66
DSUs [Member] | Non-Executive [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual compensation received for service			44,772
Units granted under the directors deferred unit plan			12,985
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of awards granted			$ 33.31	43.30
Unrecognized compensation expense			$ 24,708
Unrecognized compensation expense, years			10 months 24 days
Dividend participation rights issued			49,713
Charges to retained earnings, net of estimated forfeitures			$ 1,772
PRSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of awards granted			$ 35.44	46.63
Unrecognized compensation expense			$ 3,920
Unrecognized compensation expense, years			1 year
Descriptions of vesting period			PRSUs will vest on a single date approximately three years following the date of the grant
Vesting period			3 years
PRSUs target share distribution for Class A common stock, description			The target number of shares of common stock subject to each PRSU is one; however, based on the achievement of the performance criteria, the number of shares of common stock that may be received in connection with each PRSU generally can range from zero to two times the target number for awards granted prior to February 2021. For awards granted beginning in February 2021, based on both the performance-based and market-based criteria, the number of shares of common stock can range from zero to 2.4 times the target number.
Profits Interest Participation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock conversion basis			one-for-one
Weighted-average grant date fair value of awards granted			$ 34.53	$ 44.73
Unrecognized compensation expense			$ 27,687
Unrecognized compensation expense, years			10 months 24 days
Descriptions of vesting period			Profits interest participation rights generally provide for vesting approximately three years following the grant date
Vesting period			3 years
PRSUs target share distribution for Class A common stock, description			The target number of shares of common stock subject to each PRPU is one. Based on the achievement of performance criteria, as determined by the Compensation Committee, the number of shares of common stock that may be received in connection with the PRPU awards granted in February 2019 and February 2020 will range from zero to two times the target number. For the PRPU awards granted beginning in February 2021, subject to both performance-based and incremental market-based criteria, the number of shares will range from zero to 2.4 times the target number.
Percentage of target number of shares subject to the applicable units no longer subject to forfeiture due to threshold level of performance being achieved			25.00%
Common Stock [Member] | RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Withholding taxes in lieu of share delivery			1,514,142
Delivery of common stock associated with stock awards			2,591,484
Common Stock [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Withholding taxes in lieu of share delivery			198,455
Delivery of common stock associated with stock awards			375,205
Common Stock [Member] | 2018 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized pertaining to share based compensation arrangements		30,000,000
Share-based compensation arrangement by share-based payment award, number of additional shares authorized	20,000,000
Common Stock [Member] | Awarded Under 2008 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of outstanding common stock available under the plan		30.00%
Compensation plan expiration period		Apr. 24, 2018
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			25,000,000