Other Revenues and Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other revenues and expenses
Net gain on sale of divested business	$ 15,638	$ 0	$ 0
Contingent liability adjustment	$ (2,139)	$ 200	2,055
Cowen Equity Finance [Member]
Other revenues and expenses
Contingent liability adjustment			(2,100)
Orchard Square Partners [Member]
Other revenues and expenses
Net gain on sale of divested business			$ 4,500