Financial Derivatives (Credit Default Swaps) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Financial derivatives–assets, at fair value-	$ 15,976	$ 15,479
Financial derivatives–liabilities, at fair value-	(14,119)	(24,553)
Fair Value	(1,857)	9,074
Credit default swaps on asset-backed indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	1,599	2,184
Financial derivatives–liabilities, at fair value-	(38)	(130)
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	(1)	(1)
Financial derivatives–liabilities, at fair value-	$ 0	$ 0
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short | Weighted Average
Derivative [Line Items]
Remaining Years to Maturity	28 years 3 months	29 years
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	$ (12,298)	$ (12,888)
Financial derivatives–assets, at fair value-	$ 1,591	$ 2,179
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short | Weighted Average
Derivative [Line Items]
Remaining Years to Maturity	40 years 6 months 18 days	39 years 7 months 9 days
Credit default swaps on asset-backed securities
Derivative [Line Items]
Financial derivatives–assets, at fair value-	$ 303	$ 347
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	(909)	(957)
Financial derivatives–assets, at fair value-	$ 303	$ 347
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short | Weighted Average
Derivative [Line Items]
Remaining Years to Maturity	13 years 11 months 15 days	14 years 8 months 12 days
Credit default swaps
Derivative [Line Items]
Notional Amount	$ (36,435)	$ (66,390)
Fair Value	$ 18	$ 1,364
Credit default swaps | Weighted Average
Derivative [Line Items]
Remaining Years to Maturity	16 years 8 months 1 day	10 years 3 months
Credit default swaps on corporate bond indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	$ 174	$ 3,420
Financial derivatives–liabilities, at fair value-	(1,955)	(6,438)
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	(22,622)	(110,624)
Financial derivatives–liabilities, at fair value-	$ (1,955)	$ (6,438)
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short | Weighted Average
Derivative [Line Items]
Remaining Years to Maturity	4 years 6 months 14 days	2 years 9 months 10 days
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	$ 0	$ (2,173)
Financial derivatives–assets, at fair value-	$ 0	$ 124
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short | Weighted Average
Derivative [Line Items]
Remaining Years to Maturity	0 days	2 years 11 months 19 days