Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Interest rate swaps
Derivative [Line Items]
Average Monthly Notional	$ 795,247	$ 1,009,110
TBA securities
Derivative [Line Items]
Average Monthly Notional	1,017,245	713,634
Credit default swaps
Derivative [Line Items]
Average Monthly Notional	190,584	277,990
Total return swaps
Derivative [Line Items]
Average Monthly Notional	4,181	6,975
Futures
Derivative [Line Items]
Average Monthly Notional	180,400	149,538
Options
Derivative [Line Items]
Average Monthly Notional	0	1,500
Forwards
Derivative [Line Items]
Average Monthly Notional	24,177	26,413
Warrants
Derivative [Line Items]
Average Monthly Notional	$ 1,897	$ 1,570