Investments - Company's Investments and Securities Sold, Not Yet Purchased (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Investments	$ 541,911	$ 620,352
Alternative Investment Funds [Member]
Schedule of Investments [Line Items]
Investments	67,600	34,705
Debt Funds [Member]
Schedule of Investments [Line Items]
Investments	67,134	82,889
Equity Funds [Member]
Schedule of Investments [Line Items]
Investments	197,787	228,209
Lazard Fund Interests [Member] | Alternative Investment Funds [Member]
Schedule of Investments [Line Items]
Investments	10,996	8,321
Lazard Fund Interests [Member] | Debt Funds [Member]
Schedule of Investments [Line Items]
Investments	31,598	42,070
Lazard Fund Interests [Member] | Equity Funds [Member]
Schedule of Investments [Line Items]
Investments	$ 156,081	$ 162,798