Financial Derivatives (Futures) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Fair Value	$ 1,857	$ (9,074)
Financial derivatives–assets, at fair value-	15,976	15,479
Derivative Liability	$ 14,119	24,553
Futures
Derivative [Line Items]
Remaining Years to Maturity	3 months 3 days
Financial derivatives–assets, at fair value-	$ 1,440	2
Derivative Liability	93	376
Short | Futures
Derivative [Line Items]
Notional Amount	219,500	176,600
Fair Value	1,347	$ (374)
Remaining Years to Maturity		2 months 26 days
Financial Derivatives - Liabilities | Short | U.S. Treasury futures
Derivative [Line Items]
Notional Amount	$ 0	$ 178,200
Remaining Years to Maturity	2 months 23 days	2 months 26 days
Derivative Liability	$ 0	$ (367)
Financial Derivatives - Liabilities | Long | U.S. Treasury futures
Derivative [Line Items]
Notional Amount	$ 1,900	$ 1,900
Remaining Years to Maturity	0 years	2 months 19 days
Derivative Liability	$ (93)	$ (9)
Financial Derivatives - Assets | Short | U.S. Treasury futures
Derivative [Line Items]
Notional Amount	$ 221,400	$ 300
Remaining Years to Maturity	3 months 3 days	2 months 19 days
Financial derivatives–assets, at fair value-	$ 1,440	$ 2
Financial Derivatives - Assets | Long | U.S. Treasury futures
Derivative [Line Items]
Remaining Years to Maturity	2 months 23 days