Investments - Company's Investments and Securities Sold, Not Yet Purchased (Parenthetical) (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Investments	$ 382,074	$ 459,422
Alternative Investment Funds [Member]
Schedule of Investments [Line Items]
Investments	31,046	32,441
Alternative Investment Funds [Member] | Lazard Fund Interests [Member]
Schedule of Investments [Line Items]
Investments	11,085	13,080
Debt Funds [Member]
Schedule of Investments [Line Items]
Investments	61,486	74,597
Debt Funds [Member] | Lazard Fund Interests [Member]
Schedule of Investments [Line Items]
Investments	24,004	37,869
Equity Funds [Member]
Schedule of Investments [Line Items]
Investments	135,926	188,268
Equity Funds [Member] | Lazard Fund Interests [Member]
Schedule of Investments [Line Items]
Investments	$ 71,552	$ 128,219