Financial Derivatives (Credit Default Swaps) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Financial derivatives–assets, at fair value-	$ 15,479	$ 16,788	$ 20,001
Financial derivatives–liabilities, at fair value-	(24,553)	(27,621)	$ (20,806)
Fair Value	9,074	10,833
Credit default swaps on asset-backed indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	2,184	3,319
Financial derivatives–liabilities, at fair value-	(130)	(250)
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	(395)	(695)
Financial derivatives–assets, at fair value-	5	10
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	(12,888)	(63,515)
Financial derivatives–assets, at fair value-	2,179	3,309
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional Amount	(479)	(344)
Financial derivatives–liabilities, at fair value-	(130)	(145)
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	(1)	(4,501)
Financial derivatives–liabilities, at fair value-	0	(105)
Credit default swaps on asset-backed securities
Derivative [Line Items]
Financial derivatives–assets, at fair value-	347	993
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	(957)	(2,640)
Financial derivatives–assets, at fair value-	347	993
Credit default swaps on corporate bonds
Derivative [Line Items]
Financial derivatives–assets, at fair value-	0	2
Financial derivatives–liabilities, at fair value-	(747)	(1,693)
Credit default swaps on corporate bonds | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	0	(430)
Financial derivatives–assets, at fair value-	0	2
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	(8,400)	(10,800)
Financial derivatives–liabilities, at fair value-	(747)	(1,693)
Credit default swaps
Derivative [Line Items]
Notional Amount	(66,390)	(201,365)
Fair Value	1,364	6,554
Credit default swaps on corporate bond indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	3,420	5,599
Financial derivatives–liabilities, at fair value-	(6,438)	(14,524)
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	(67,779)	(130,707)
Financial derivatives–assets, at fair value-	3,296	5,547
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	(2,173)	(1,997)
Financial derivatives–assets, at fair value-	124	52
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	(110,624)	(250,088)
Financial derivatives–liabilities, at fair value-	$ (6,438)	$ (14,524)
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	16 years 11 months 26 days	23 years 9 months 18 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	39 years 7 months 9 days	38 years 4 months 24 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Remaining Years to Maturity	32 years 4 months 9 days	29 years 4 months 6 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	29 years	40 years 3 months 21 days
Weighted Average | Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	14 years 8 months 12 days	15 years 7 months 17 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	0 days	5 months 19 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	4 years 2 months 1 day	3 years 11 months 1 day
Weighted Average | Credit default swaps
Derivative [Line Items]
Remaining Years to Maturity	10 years 3 months	14 years 10 months 17 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	2 years 6 months 7 days	2 years 5 months 1 day
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	2 years 11 months 19 days	3 years 11 months 19 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	2 years 9 months 10 days	2 years 6 months 3 days