Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Interest rate swaps
Derivative [Line Items]
Average Monthly Notional	$ 1,194,366	$ 731,941
TBA securities
Derivative [Line Items]
Average Monthly Notional	969,311	973,331
Credit default swaps
Derivative [Line Items]
Average Monthly Notional	328,023	399,316
Total return swaps
Derivative [Line Items]
Average Monthly Notional	12,626	39,434
Futures
Derivative [Line Items]
Average Monthly Notional	110,200	167,708
Options
Derivative [Line Items]
Average Monthly Notional	4,876	19,825
Forwards
Derivative [Line Items]
Average Monthly Notional	35,847	30,930
Warrants
Derivative [Line Items]
Average Monthly Notional	$ 1,538	$ 2,222