Senior Debt - Senior Debt (Parenthetical) (Detail) - USD ($)		3 Months Ended
	Apr. 10, 2019	Mar. 31, 2019
Debt Instrument [Line Items]
Redemption of senior debt aggregate principal amount		$ 167,943,000
Subsequent Event [Member]
Debt Instrument [Line Items]
Redemption of senior debt aggregate principal amount	$ 82,057,000
Lazard Group 4.375% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount		$ 500,000,000
Interest rate, payment terms		Interest on the 2029 Notes is payable semi-annually on March 11 and September 11 of each year, beginning September 11, 2019.
Senior notes interest rate		4.375%
Original Maturity Date		Mar. 11, 2029
Effective interest rates of senior notes		4.54%
Lazard Group 4.25% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount		$ 500,000,000
Senior notes interest rate		4.25%
Redemption of senior debt aggregate principal amount		$ 250,000,000
Original Maturity Date		Nov. 14, 2020
Lazard Group 3.75% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount		$ 400,000,000
Senior notes interest rate		3.75%
Original Maturity Date		Feb. 13, 2025
Effective interest rates of senior notes		3.87%
Lazard Group 3.625% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount		$ 300,000,000
Senior notes interest rate		3.625%
Original Maturity Date		Mar. 01, 2027
Effective interest rates of senior notes		3.76%
Lazard Group 4.50% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount		$ 500,000,000
Senior notes interest rate		4.50%
Original Maturity Date		Sep. 19, 2028
Effective interest rates of senior notes		4.68%