Related Party Transactions (Schedule Of Related Party Transactions) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Related Party Transaction [Line Items]
Net trading	$ 18,561	$ 8,724
Principal transactions and other income	(2,406)	414
Income (loss) from equity method affiliates	(107)	(8)
TBBK [Member]
Related Party Transaction [Line Items]
Net trading		2
EuroDekania Management Limited [Member]
Related Party Transaction [Line Items]
Asset management		86
Principal transactions and other income		291
Fin Tech Acquisition Corp II [Member]
Related Party Transaction [Line Items]
Principal transactions and other income	3	3
Insurance SPAC [Member]
Related Party Transaction [Line Items]
Principal transactions and other income	30	4
Income (loss) from equity method affiliates	(307)	(8)
SPAC Funds [Member]
Related Party Transaction [Line Items]
Asset management	(47)	31
Principal transactions and other income	(59)	24
U.S. Insurance JV [Member]
Related Party Transaction [Line Items]
Asset management	90	80
Principal transactions and other income	(167)	39
AOI [Member]
Related Party Transaction [Line Items]
Income (loss) from equity method affiliates	(30)
CK Capital Partners B.V. [Member]
Related Party Transaction [Line Items]
Income (loss) from equity method affiliates	230
Duane Morris [Member]
Related Party Transaction [Line Items]
Operating expense (income)	319	101
FinTech Masala [Member]
Related Party Transaction [Line Items]
Operating expense (income)	11	6
CBF [Member]
Related Party Transaction [Line Items]
Interest expense (income)	528	119
DGC Trust [Member]
Related Party Transaction [Line Items]
Interest expense (income)	533	390
E.B.C. [Member]
Related Party Transaction [Line Items]
Interest expense (income)	72	47
Edward E. Cohen IRA [Member]
Related Party Transaction [Line Items]
Interest expense (income)	48	87
JKD Capital Partners I, LTD [Member]
Related Party Transaction [Line Items]
Interest expense (income)	484	278
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Asset management	43	197
Principal transactions and other income	(193)	361
Income (loss) from equity method affiliates	(107)	(8)
Operating expense (income)	308	95
Interest expense (income)	$ 1,665	$ 921