Securities Owned and Sold, Not Yet Purchased (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Securities owned and sold, not yet purchased
Securities owned, at fair value	$ 21,943	$ 7,436
Securities sold, not yet purchased, at fair value	22,856	2,953
Corporate stocks-trading securities
Securities owned and sold, not yet purchased
Securities owned, at fair value	17,867	2,894
Securities sold, not yet purchased, at fair value	22,856	2,953
Mutual funds
Securities owned and sold, not yet purchased
Securities owned, at fair value	$ 4,076	$ 4,542