Securities Owned and Sold, Not Yet Purchased (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Securities owned and sold, not yet purchased
Securities owned, at fair value	$ 2,557	$ 5,598
Securities sold, not yet purchased, at fair value	249	2,637
Corporate stocks-trading securities
Securities owned and sold, not yet purchased
Securities owned, at fair value	244	2,571
Securities sold, not yet purchased, at fair value	249	2,637
Mutual funds
Securities owned and sold, not yet purchased
Securities owned, at fair value	$ 2,313	$ 3,027