Financial Derivatives (Credit Default Swaps) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Financial derivatives–assets, at fair value-		$ 27,864	$ 16,788
Financial derivatives–liabilities, at fair value-		(34,814)	(27,621)
Fair Value		6,950	10,833
Credit default swaps on asset-backed indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-		9,722	3,319
Financial derivatives–liabilities, at fair value-		(142)	(250)
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount		(416)	(695)
Financial derivatives–assets, at fair value-		6	10
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount		(30,668)	(63,515)
Financial derivatives–assets, at fair value-		9,716	3,309
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional Amount		(480)	(344)
Financial derivatives–liabilities, at fair value-		(142)	(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-		351	993
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount		(955)	(2,640)
Financial derivatives–assets, at fair value-		351	993
Credit default swaps on corporate bonds
Derivative [Line Items]
Financial derivatives–assets, at fair value-		39	2
Financial derivatives–liabilities, at fair value-		(580)	(1,693)
Credit default swaps on corporate bonds | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount		(1,600)	(430)
Financial derivatives–assets, at fair value-		39	2
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount		(12,200)	(10,800)
Financial derivatives–liabilities, at fair value-		(580)	(1,693)
Credit default swaps on corporate bond indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-		2,419	5,599
Financial derivatives–liabilities, at fair value-		(3,572)	(14,524)
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount		(69,381)	(130,707)
Financial derivatives–assets, at fair value-		1,913	5,547
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount		(10,036)	(1,997)
Financial derivatives–assets, at fair value-		506	52
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount		(126,983)	(250,088)
Financial derivatives–liabilities, at fair value-		(3,572)	(14,524)
Credit default swaps
Derivative [Line Items]
Notional Amount		(108,966)	(201,365)
Fair Value		$ (8,237)	$ 6,554
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity		17 years 3 months	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		37 years 8 months 15 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 7 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 3 months	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 11 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 - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	0 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity		3 years 8 months 15 days	3 years 11 months 1 day
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity		2 years 8 months 15 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		1 year 7 months 20 days	3 years 11 months 19 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Remaining Years to Maturity	0 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity		2 years 25 days	2 years 6 months 3 days
Weighted Average | Credit default swaps
Derivative [Line Items]
Remaining Years to Maturity		11 years 8 months 15 days	14 years 10 months 17 days