Financial Derivatives (Schedule of Financial Derivatives) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	$ 15,479	$ 16,788	$ 20,001
Financial derivatives–liabilities, at fair value-	(24,553)	(27,621)	$ (20,806)
Total	(9,074)	(10,833)
TBA Securities, Purchase Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	961	90
TBA Securities, Sale Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	1	506
Financial derivatives–liabilities, at fair value-	(925)	(1,012)
Interest rate swaps | Short
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	125	3,914
Financial derivatives–liabilities, at fair value-	(15,109)	(8,513)
Interest rate swaps | Long
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	8,394	1,554
Financial derivatives–liabilities, at fair value-	(65)	(206)
Credit default swaps on asset-backed securities
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	347	993
Credit default swaps on asset-backed indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	2,184	3,319
Financial derivatives–liabilities, at fair value-	(130)	(250)
Credit default swaps on corporate bonds
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	0	2
Financial derivatives–liabilities, at fair value-	(747)	(1,693)
Credit default swaps on corporate bond indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	3,420	5,599
Financial derivatives–liabilities, at fair value-	(6,438)	(14,524)
Total return swaps
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	9	620
Financial derivatives–liabilities, at fair value-	(484)	(1,209)
Futures
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	2	148
Financial derivatives–liabilities, at fair value-	(376)	(45)
Futures | Short
Derivatives, Fair Value [Line Items]
Total	(374)	103
Forwards
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	0	43
Financial derivatives–liabilities, at fair value-	(279)	(169)
Warrants
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	$ 36	$ 0