Financial Derivatives (Schedule of Credit Derivatives) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Credit Derivatives [Line Items]
Financial derivatives–assets, at fair value-	$ 23,082	$ 15,479
Derivative Liability	(19,438)	(24,553)
Derivative Assets (Liabilities), at Fair Value, Net	3,644	(9,074)
Credit default swaps on asset-backed indices
Credit Derivatives [Line Items]
Financial derivatives–assets, at fair value-	2,087	2,184
Derivative Liability	(127)	(130)
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Credit Derivatives [Line Items]
Notional value	555	395
Financial derivatives–assets, at fair value-	$ 6	$ 5
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	24 years 3 days	16 years 11 months 26 days
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Credit Derivatives [Line Items]
Notional value	$ 13,705	$ 12,888
Financial derivatives–assets, at fair value-	$ 2,081	$ 2,179
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	43 years 11 months 19 days	39 years 7 months 9 days
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Credit Derivatives [Line Items]
Notional value	$ 293	$ 479
Derivative Liability	$ (127)	$ (130)
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	28 years 10 days	32 years 4 months 9 days
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Credit Derivatives [Line Items]
Notional value	$ 1	$ 1
Derivative Liability	$ 0	$ 0
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	28 years 9 months 3 days	29 years
Credit default swaps on corporate bond indices
Credit Derivatives [Line Items]
Financial derivatives–assets, at fair value-	$ 3,427	$ 3,420
Derivative Liability	(5,128)	(6,438)
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Credit Derivatives [Line Items]
Notional value	67,354	67,779
Financial derivatives–assets, at fair value-	$ 3,422	$ 3,296
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	2 years 3 months 7 days	2 years 6 months 7 days
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Credit Derivatives [Line Items]
Notional value	$ 1,642	$ 2,173
Financial derivatives–assets, at fair value-	$ 5	$ 124
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	2 years 8 months 19 days	2 years 11 months 19 days
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Credit Derivatives [Line Items]
Notional value	$ 93,661	$ 110,624
Derivative Liability	$ (5,128)	$ (6,438)
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	2 years 3 months 29 days	2 years 9 months 10 days
Credit default swaps on asset-backed securities
Credit Derivatives [Line Items]
Financial derivatives–assets, at fair value-	$ 320	$ 347
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Credit Derivatives [Line Items]
Notional value	927	957
Financial derivatives–assets, at fair value-	$ 320	$ 347
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	14 years 5 months 15 days	14 years 8 months 12 days
Credit default swaps on corporate bonds
Credit Derivatives [Line Items]
Derivative Liability	$ (682)	$ (747)
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Credit Derivatives [Line Items]
Notional value	8,400	8,400
Derivative Liability	$ (682)	$ (747)
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	3 years 11 months 4 days	4 years 2 months 1 day
Credit default swaps
Credit Derivatives [Line Items]
Notional value	$ 50,134	$ 66,390
Derivative Assets (Liabilities), at Fair Value, Net	$ (103)	$ (1,364)
Credit default swaps | Weighted Average
Credit Derivatives [Line Items]
Remaining Years to Maturity	13 years 10 months 24 days	10 years 3 months
Credit Default Swap, Selling Protection [Member]
Credit Derivatives [Line Items]
Fair Value	$ 3,301	$ 3,171
Notional value	$ 68,202	$ 68,653