Investments - Company's Investments and Securities Sold, Not Yet Purchased (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Debt (including interest-bearing deposits of $516 and $578, respectively)	$ 8,529	$ 5,948
Equities	59,394	44,992
Funds	400,694	356,721
Equity method	9,488	7,012
Total investments	478,105	414,673
Interest-bearing deposits	516	578
Investments, at fair value	468,101	407,083
Securities sold, not yet purchased, at fair value (included in "other liabilities")	4,045	2,755
Debt Funds [Member]
Schedule of Investments [Line Items]
Funds	58,769	32,077
Alternative Investments Funds [Member]
Schedule of Investments [Line Items]
Funds	37,030	57,890
Equity Funds [Member]
Schedule of Investments [Line Items]
Funds	190,702	154,310
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Funds	$ 114,193	$ 112,444