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 |