Investments - Company's Investments and Securities Sold, Not Yet Purchased (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Interest-bearing deposits	$ 578	$ 2,834
Lazard fund interests in equities	76,907	19,857
Lazard fund interests in alternative investments	5,054	5,367
Lazard fund interest in debt	$ 18,615	$ 2,101