Financial Derivatives (Credit Default Swaps) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Financial derivatives–assets, at fair value-	$ 12,740	$ 20,001
Financial derivatives–liabilities, at fair value-	(25,572)	$ (20,806)
Fair Value	12,832
Credit default swaps on asset-backed indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	2,146
Financial derivatives–liabilities, at fair value-	(194)
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	729
Financial derivatives–assets, at fair value-	9
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	25,960
Financial derivatives–assets, at fair value-	2,137
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional Amount	361
Financial derivatives–liabilities, at fair value-	(155)
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	4,500
Financial derivatives–liabilities, at fair value-	(39)
Credit default swaps on asset-backed securities
Derivative [Line Items]
Financial derivatives–assets, at fair value-	1,078
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	2,750
Financial derivatives–assets, at fair value-	1,078
Credit default swaps on corporate bonds
Derivative [Line Items]
Financial derivatives–assets, at fair value-	41
Financial derivatives–liabilities, at fair value-	(186)
Credit default swaps on corporate bonds | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	430
Financial derivatives–assets, at fair value-	2
Credit default swaps on corporate bonds | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	2,118
Financial derivatives–assets, at fair value-	39
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional Amount	2,114
Financial derivatives–liabilities, at fair value-	(58)
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	7,500
Financial derivatives–liabilities, at fair value-	(128)
Credit default swaps on corporate bond indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	5,060
Financial derivatives–liabilities, at fair value-	(11,185)
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional Amount	130,743
Financial derivatives–assets, at fair value-	4,920
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional Amount	1,940
Financial derivatives–assets, at fair value-	140
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional Amount	218,547
Financial derivatives–liabilities, at fair value-	(11,185)
Credit default swaps
Derivative [Line Items]
Notional Amount	128,938
Fair Value	$ 3,240
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	23 years 285 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	37 years 18 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Remaining Years to Maturity	29 years 226 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	40 years 208 days
Weighted Average | Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	15 years 329 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	263 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	190 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Remaining Years to Maturity	208 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	210 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	2 years 248 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	4 years 80 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	2 years 146 days
Weighted Average | Credit default swaps
Derivative [Line Items]
Remaining Years to Maturity	10 years 161 days