Investments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Lazard Fund Interests in Equities	$ 76,280	$ 19,857
Lazard Fund Interests in alternative asset management funds	3,577	2,256
Lazard Fund Interests in fixed income funds	21,856	5,212
Economic interests that are owned by management team and other investors in the Edgewater Funds	$ 19,734	$ 18,502