Senior Debt (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Senior debt, Outstanding	$ 1,076,850	$ 1,076,850
Lazard Group 7.125% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	550,000
Senior Debt, Maturity Date	May 15, 2015
Senior Debt, Annual Interest Rate	7.125%
Senior debt, Outstanding	528,500	528,500
Lazard Group 6.85% Senior Notes [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	600,000
Senior Debt, Maturity Date	Jun. 15, 2017
Senior Debt, Annual Interest Rate	6.85%
Senior debt, Outstanding	548,350	548,350
Lazard Group Credit Facility [Member]
Debt Instrument [Line Items]
Senior Debt, Initial Principal Amount	$ 150,000
Senior Debt, Maturity Date	Sep. 25, 2015
Senior Debt, Annual Interest Rate	0.90%