Investments - Company's Investments and Securities Sold, Not Yet Purchased (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Debt (including interest-bearing deposits of $533 and $516, respectively)	$ 7,806	$ 8,529
Equities	57,757	59,394
Funds	343,180	400,694
Equity method	8,552	9,488
Total investments	417,295	478,105
Interest-bearing deposits	533	516
Investments, at fair value	408,210	468,101
Securities sold, not yet purchased, at fair value (included in "other liabilities")	5,330	4,045
Debt Funds [Member]
Schedule of Investments [Line Items]
Funds	48,207	58,769
Alternative Investments Funds [Member]
Schedule of Investments [Line Items]
Funds	36,321	37,030
Equity Funds [Member]
Schedule of Investments [Line Items]
Funds	143,115	190,702
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Funds	$ 115,537	$ 114,193