Senior Debt - Senior Debt (Detail) - USD ($)	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Senior Debt, Outstanding Principal	$ 1,700,000,000	$ 1,700,000,000
Senior Debt, Outstanding Unamortized Debt Costs	16,016,000	17,259,000
Senior Debt, Outstanding Carrying Value	1,683,984,000	1,682,741,000
Lazard Group 3.75% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 400,000,000
Senior Debt, Maturity Date	Feb. 13, 2025
Senior Debt, Annual Interest Rate	3.75%
Senior Debt, Outstanding Principal	$ 400,000,000	400,000,000
Senior Debt, Outstanding Unamortized Debt Costs	1,712,000	1,948,000
Senior Debt, Outstanding Carrying Value	398,288,000	398,052,000
Lazard Group 3.625% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 300,000,000
Senior Debt, Maturity Date	Mar. 01, 2027
Senior Debt, Annual Interest Rate	3.625%
Senior Debt, Outstanding Principal	$ 300,000,000	300,000,000
Senior Debt, Outstanding Unamortized Debt Costs	2,210,000	2,405,000
Senior Debt, Outstanding Carrying Value	297,790,000	297,595,000
Lazard Group 4.50% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 500,000,000
Senior Debt, Maturity Date	Sep. 19, 2028
Senior Debt, Annual Interest Rate	4.50%
Senior Debt, Outstanding Principal	$ 500,000,000	500,000,000
Senior Debt, Outstanding Unamortized Debt Costs	6,142,000	6,568,000
Senior Debt, Outstanding Carrying Value	493,858,000	493,432,000
Lazard Group 4.375% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 500,000,000
Senior Debt, Maturity Date	Mar. 11, 2029
Senior Debt, Annual Interest Rate	4.375%
Senior Debt, Outstanding Principal	$ 500,000,000	500,000,000
Senior Debt, Outstanding Unamortized Debt Costs	5,952,000	6,338,000
Senior Debt, Outstanding Carrying Value	$ 494,048,000	$ 493,662,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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