Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest rate swaps
Derivative [Line Items]
Average Monthly Notional	$ 1,009,110	$ 731,941	$ 1,059,756
TBA securities
Derivative [Line Items]
Average Monthly Notional	713,634	973,331
Credit default swaps
Derivative [Line Items]
Average Monthly Notional	277,990	399,316	566,805
Total return swaps
Derivative [Line Items]
Average Monthly Notional	6,975	39,434	53,603
Futures
Derivative [Line Items]
Average Monthly Notional	149,538	167,708	201,295
Options
Derivative [Line Items]
Average Monthly Notional	1,500	19,825	99,891
Forwards
Derivative [Line Items]
Average Monthly Notional	26,413	30,930	$ 45,522
Warrants
Derivative [Line Items]
Average Monthly Notional	$ 1,570	$ 2,222