Financial Derivatives (Credit Default Swaps) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Financial derivatives–assets, at fair value-	$ 31,752	$ 16,788
Financial derivatives–liabilities, at fair value-	(47,772)	(27,621)
Fair Value	16,020	10,833
Credit default swaps on asset-backed indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	14,276	3,319
Financial derivatives–liabilities, at fair value-	(162)	(250)
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	(474)	(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	(63,528)	(63,515)
Financial derivatives–assets, at fair value-	14,271	3,309
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional Amount	(523)	(344)
Financial derivatives–liabilities, at fair value-	(162)	(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-	353	993
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	(998)	(2,640)
Financial derivatives–assets, at fair value-	353	993
Credit default swaps on corporate bonds
Derivative [Line Items]
Financial derivatives–assets, at fair value-	1,202	2
Financial derivatives–liabilities, at fair value-	(62)	(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 - Assets | Short
Derivative [Line Items]
Notional Amount	(6,200)	0
Financial derivatives–assets, at fair value-	1,202	0
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional Amount	(430)	0
Financial derivatives–liabilities, at fair value-	(3)	0
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	(2,800)	(10,800)
Financial derivatives–liabilities, at fair value-	(59)	(1,693)
Credit default swaps on corporate bond indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	3,732	5,599
Financial derivatives–liabilities, at fair value-	(1,922)	(14,524)
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	(32,159)	(130,707)
Financial derivatives–assets, at fair value-	11	5,547
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	(73,826)	(1,997)
Financial derivatives–assets, at fair value-	3,721	52
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional Amount	(40,438)	0
Financial derivatives–liabilities, at fair value-	(1,843)	0
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	(57,518)	(250,088)
Financial derivatives–liabilities, at fair value-	(79)	(14,524)
Credit default swaps
Derivative [Line Items]
Notional Amount	(130,847)	(201,365)
Fair Value	$ (17,417)	$ 6,554
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	17 years 9 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 12 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 9 months 14 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 9 months 3 days	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	15 years 5 months 15 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	4 years 8 months 23 days	0 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Remaining Years to Maturity	2 months 19 days	0 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	8 months 1 day	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 19 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 12 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	3 years 7 months 2 days	0 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	1 year 8 months 26 days	2 years 6 months 3 days
Weighted Average | Credit default swaps
Derivative [Line Items]
Remaining Years to Maturity	19 years 1 month 9 days	14 years 10 months 17 days