Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Interest rate swaps
Derivative [Line Items]
Average Monthly Notional	$ 730,908	$ 1,059,756
TBA securities
Derivative [Line Items]
Average Monthly Notional	1,087,157
Credit default swaps
Derivative [Line Items]
Average Monthly Notional	410,213	566,805
Total return swaps
Derivative [Line Items]
Average Monthly Notional	39,779	53,603
Futures
Derivative [Line Items]
Average Monthly Notional	199,246	201,295
Options
Derivative [Line Items]
Average Monthly Notional	25,772	99,891
Forwards
Derivative [Line Items]
Average Monthly Notional	33,360	$ 45,522
Warrants
Derivative [Line Items]
Average Monthly Notional	$ 2,281