Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Interest rate swaps
Derivative [Line Items]
Average Monthly Notional	$ 1,078,808	$ 731,941
TBA securities
Derivative [Line Items]
Average Monthly Notional	732,048	973,331
Credit default swaps
Derivative [Line Items]
Average Monthly Notional	290,822	399,316
Total return swaps
Derivative [Line Items]
Average Monthly Notional	7,819	39,434
Futures
Derivative [Line Items]
Average Monthly Notional	143,440	167,708
Options
Derivative [Line Items]
Average Monthly Notional	1,950	19,825
Forwards
Derivative [Line Items]
Average Monthly Notional	36,935	30,930
Warrants
Derivative [Line Items]
Average Monthly Notional	$ 1,543	$ 2,222