Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Interest rate swaps
Derivative [Line Items]
Average Monthly Notional	$ 1,126,497	$ 1,009,110
TBA securities
Derivative [Line Items]
Average Monthly Notional	1,083,070	713,634
Credit default swaps
Derivative [Line Items]
Average Monthly Notional	130,899	277,990
Total return swaps
Derivative [Line Items]
Average Monthly Notional	3,372	6,975
Futures
Derivative [Line Items]
Average Monthly Notional	184,690	149,538
Options
Derivative [Line Items]
Average Monthly Notional	12,000	1,500
Forwards
Derivative [Line Items]
Average Monthly Notional	22,498	26,413
Warrants
Derivative [Line Items]
Average Monthly Notional	$ 1,956	$ 1,570