Financial Derivatives (Schedule of Financial Derivatives) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	$ 11,150	$ 20,001
Financial derivatives–liabilities, at fair value-	(27,805)	$ (20,806)
Total	(16,655)
TBA Securities, Purchase Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	121
TBA Securities, Sale Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	19
Financial derivatives–liabilities, at fair value-	(2,443)
Interest rate swaps | Short
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	31
Financial derivatives–liabilities, at fair value-	(7,658)
Interest rate swaps | Long
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	1,403
Credit default swaps on asset-backed securities
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	1,090
Credit default swaps on asset-backed indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	2,164
Financial derivatives–liabilities, at fair value-	(202)
Credit default swaps on corporate bonds
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	521
Financial derivatives–liabilities, at fair value-	(686)
Credit default swaps on corporate bond indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	5,714
Financial derivatives–liabilities, at fair value-	(14,113)
Total return swaps
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	87
Financial derivatives–liabilities, at fair value-	(58)
Futures
Derivatives, Fair Value [Line Items]
Financial derivatives–liabilities, at fair value-	(2,380)
Futures | Short
Derivatives, Fair Value [Line Items]
Total	(2,380)
Forwards
Derivatives, Fair Value [Line Items]
Financial derivatives–liabilities, at fair value-	$ (265)