Financial Derivatives (Futures) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Fair Value	$ 3,644	$ (9,074)
Financial derivatives–assets, at fair value-	23,082	15,479
Derivative Liability	19,438	24,553
Futures
Derivative [Line Items]
Financial derivatives–assets, at fair value-	2,704	2
Derivative Liability	163	376
Short | Futures
Derivative [Line Items]
Notional Amount	176,600	176,600
Fair Value	$ 2,541	$ (374)
Remaining Years to Maturity	3 months	2 months 26 days
Financial Derivatives - Liabilities | Short | U.S. Treasury futures
Derivative [Line Items]
Notional Amount	$ 0	$ 178,200
Remaining Years to Maturity	0 years	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	2 months 23 days	2 months 19 days
Derivative Liability	$ (163)	$ (9)
Financial Derivatives - Assets | Short | U.S. Treasury futures
Derivative [Line Items]
Notional Amount	$ 178,500	$ 300
Remaining Years to Maturity	3 months	2 months 19 days
Financial derivatives–assets, at fair value-	$ 2,704	$ 2