Organization and Basis of Presentation - Additional Information (Detail)	1 Months Ended	9 Months Ended
	May. 31, 2014 $ / shares shares	Sep. 30, 2015 Segment $ / shares shares	Dec. 31, 2014 $ / shares shares	Sep. 30, 2014 shares	Jan. 01, 2014 shares	Dec. 31, 2013
Organization And Basis Of Presentation [Line Items]
Governing operating agreement, date		Oct. 26, 2015
Common stock, Class B shares conversion to Class A shares	1
Common stock conversion basis		In May 2014, the remaining outstanding Lazard Group common membership interests held by LAZ-MD Holdings were exchanged for shares of the Company’s Class A common stock, and the sole issued and outstanding share of the Company’s Class B common stock was automatically converted into one share of the Company’s Class A common stock pursuant to the provisions of the Company’s bye-laws, resulting in only one outstanding class of common stock (the “Final Exchange of LAZ-MDInterests”). Following the Final Exchange of LAZ-MD Interests, Lazard Group became a wholly-owned indirect subsidiary of Lazard Ltd.
Number of business segments | Segment		2
Class B Common Stock [Member]
Organization And Basis Of Presentation [Line Items]
Common stock, shares issued					1
Class A Common Stock [Member]
Organization And Basis Of Presentation [Line Items]
Common stock, par value | $ / shares	$ 0.01	$ 0.01	$ 0.01
Common stock, shares outstanding		129,766,091	129,766,091
Common stock, shares issued		129,766,091	129,766,091	129,766,091	129,056,081
LAZ-MD Holdings LLC [Member] | Class B Common Stock [Member]
Organization And Basis Of Presentation [Line Items]
Common stock, shares outstanding					1
Common stock, shares issued					1
Lazard Group Llc [Member]
Organization And Basis Of Presentation [Line Items]
Percentage of common membership interests held		100.00%	100.00%
Lazard Group Llc [Member] | LAZ-MD Holdings LLC [Member]
Organization And Basis Of Presentation [Line Items]
Percentage of common membership interests held						0.50%