Financial Derivatives (Schedule of Derivative Activity) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Interest rate swaps
Derivative [Line Items]
Average Monthly Notional	$ 774,539	$ 1,059,756
TBA securities
Derivative [Line Items]
Average Monthly Notional	1,201,858
Credit default swaps
Derivative [Line Items]
Average Monthly Notional	409,549	566,805
Total return swaps
Derivative [Line Items]
Average Monthly Notional	38,507	53,603
Futures
Derivative [Line Items]
Average Monthly Notional	239,826	201,295
Options
Derivative [Line Items]
Average Monthly Notional	36,818	99,891
Forwards
Derivative [Line Items]
Average Monthly Notional	35,530	$ 45,522
Warrants
Derivative [Line Items]
Average Monthly Notional	$ 2,281