Financial Derivatives (Schedule of Financial Derivatives) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	$ 27,864	$ 16,788
Financial derivatives–liabilities, at fair value-	(34,814)	(27,621)
Total	(6,950)	(10,833)
TBA Securities, Purchase Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	394	90
Financial derivatives–liabilities, at fair value-	(156)	0
TBA Securities, Sale Contracts [Member]
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	756	506
Financial derivatives–liabilities, at fair value-	(130)	(1,012)
Interest rate swaps | Short
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	5	3,914
Financial derivatives–liabilities, at fair value-	(29,712)	(8,513)
Interest rate swaps | Long
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	13,785	1,554
Financial derivatives–liabilities, at fair value-	(62)	(206)
Credit default swaps on asset-backed securities
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	351	993
Credit default swaps on asset-backed indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	9,722	3,319
Financial derivatives–liabilities, at fair value-	(142)	(250)
Credit default swaps on corporate bonds
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	39	2
Financial derivatives–liabilities, at fair value-	(580)	(1,693)
Credit default swaps on corporate bond indices
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	2,419	5,599
Financial derivatives–liabilities, at fair value-	(3,572)	(14,524)
Total return swaps
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	105	620
Financial derivatives–liabilities, at fair value-	(88)	(1,209)
Futures
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	1	148
Financial derivatives–liabilities, at fair value-	(331)	(45)
Futures | Short
Derivatives, Fair Value [Line Items]
Total	(330)	103
Forwards
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	256	43
Financial derivatives–liabilities, at fair value-	(41)	(169)
Warrants
Derivatives, Fair Value [Line Items]
Financial derivatives–assets, at fair value-	$ 31	$ 0