Securities Owned and Sold, Not Yet Purchased (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Securities owned and sold, not yet purchased
Securities owned, at fair value	$ 8,678	$ 5,598
Securities sold, not yet purchased, at fair value	6,143	2,637
Corporate stocks-trading securities
Securities owned and sold, not yet purchased
Securities owned, at fair value	6,171	2,571
Securities sold, not yet purchased, at fair value	6,143	2,637
Mutual funds
Securities owned and sold, not yet purchased
Securities owned, at fair value	$ 2,507	$ 3,027