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.

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

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

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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.

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Senior Debt - Senior Debt (Detail) - USD ($)	12 Months Ended
Senior Debt - Senior Debt (Detail) - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Nov. 30, 2016
Debt Instrument [Line Items]
Senior Debt, Outstanding Principal	$ 1,450,000,000		$ 1,200,000,000
Senior Debt, Outstanding Unamortized Debt Costs	15,740,000		9,617,000
Senior Debt, Outstanding Carrying Value	1,434,260,000		1,190,383,000
Lazard Group 4.25% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 500,000,000
Senior Debt, Maturity Date	Nov. 14, 2020
Senior Debt, Annual Interest Rate	4.25%	4.25%
Senior Debt, Outstanding Principal	$ 250,000,000		500,000,000
Senior Debt, Outstanding Unamortized Debt Costs	863,000		2,647,000
Senior Debt, Outstanding Carrying Value	249,137,000		497,353,000
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	2,888,000		3,361,000
Senior Debt, Outstanding Carrying Value	397,112,000		396,639,000
Lazard Group 3.625% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 300,000,000			$ 300,000,000
Senior Debt, Maturity Date	Mar. 01, 2027
Senior Debt, Annual Interest Rate	3.625%			3.625%
Senior Debt, Outstanding Principal	$ 300,000,000		300,000,000
Senior Debt, Outstanding Unamortized Debt Costs	3,215,000		3,609,000
Senior Debt, Outstanding Carrying Value	296,785,000		$ 296,391,000
Lazard Group 4.50% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 500,000,000	$ 500,000,000
Senior Debt, Maturity Date	Sep. 19, 2028
Senior Debt, Annual Interest Rate	4.50%	4.50%
Senior Debt, Outstanding Principal	$ 500,000,000
Senior Debt, Outstanding Unamortized Debt Costs	8,774,000
Senior Debt, Outstanding Carrying Value	$ 491,226,000