Financial Derivatives (Schedule of Financial Derivatives) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	$ 12,740	$ 20,001
Financial derivatives–liabilities, at fair value-	(25,572)	$ (20,806)
Total	(12,832)
TBA Securities, Purchase Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	43
TBA Securities, Sale Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	99
Financial derivatives–liabilities, at fair value-	(904)
Interest rate swaps | Short
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	1,760
Financial derivatives–liabilities, at fair value-	(12,099)
Interest rate swaps | Long
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	1,680
Financial derivatives–liabilities, at fair value-	(16)
Credit default swaps on asset-backed securities
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	1,078
Credit default swaps on asset-backed indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	2,146
Financial derivatives–liabilities, at fair value-	(194)
Credit default swaps on corporate bonds
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	41
Financial derivatives–liabilities, at fair value-	(186)
Credit default swaps on corporate bond indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	5,060
Financial derivatives–liabilities, at fair value-	(11,185)
Total return swaps
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	235
Financial derivatives–liabilities, at fair value-	(921)
Futures
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	484
Financial derivatives–liabilities, at fair value-	(67)
Futures | Short
Derivatives, Fair Value [Line Items]
Total	417
Forwards
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	$ 114