Financial Derivatives (Credit Default Swaps) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Financial derivatives–assets, at fair value-	$ 11,150	$ 20,001
Financial derivatives–liabilities, at fair value-	(27,805)	$ (20,806)
Fair Value	(16,655)
Credit default swaps on asset-backed indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	2,164
Financial derivatives–liabilities, at fair value-	(202)
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional amount, assets	794
Financial derivatives–assets, at fair value-	9
Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional amount, assets	24,492
Financial derivatives–assets, at fair value-	2,155
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional amount, liabilities	(376)
Financial derivatives–liabilities, at fair value-	164
Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional amount, liabilities	(2,500)
Financial derivatives–liabilities, at fair value-	38
Credit default swaps on asset-backed securities
Derivative [Line Items]
Financial derivatives–assets, at fair value-	1,090
Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional amount, assets	2,775
Financial derivatives–assets, at fair value-	1,090
Credit default swaps on corporate bonds
Derivative [Line Items]
Financial derivatives–assets, at fair value-	521
Financial derivatives–liabilities, at fair value-	(686)
Credit default swaps on corporate bonds | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional amount, assets	430
Financial derivatives–assets, at fair value-	2
Credit default swaps on corporate bonds | Financial Derivatives - Assets | Short
Derivative [Line Items]
Notional amount, assets	3,033
Financial derivatives–assets, at fair value-	519
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Notional amount, liabilities	(2,980)
Financial derivatives–liabilities, at fair value-	501
Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional amount, liabilities	(10,245)
Financial derivatives–liabilities, at fair value-	185
Credit default swaps on corporate bond indices
Derivative [Line Items]
Financial derivatives–assets, at fair value-	5,714
Financial derivatives–liabilities, at fair value-	(14,113)
Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Notional amount, assets	140,543
Financial derivatives–assets, at fair value-	5,714
Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Notional amount, liabilities	(238,213)
Financial derivatives–liabilities, at fair value-	14,113
Credit default swaps
Derivative [Line Items]
Notional Amount	136,135
Fair Value	$ (5,512)
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	23 years 212 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	37 years 4 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Remaining Years to Maturity	29 years 325 days
Weighted Average | Credit default swaps on asset-backed indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	38 years 120 days
Weighted Average | Credit default swaps on asset-backed securities | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	16 years 55 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	358 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Assets | Short
Derivative [Line Items]
Remaining Years to Maturity	1 year 270 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Long
Derivative [Line Items]
Remaining Years to Maturity	1 year 263 days
Weighted Average | Credit default swaps on corporate bonds | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	256 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Assets | Long
Derivative [Line Items]
Remaining Years to Maturity	3 years 29 days
Weighted Average | Credit default swaps on corporate bond indices | Financial Derivatives - Liabilities | Short
Derivative [Line Items]
Remaining Years to Maturity	2 years 281 days
Weighted Average | Credit default swaps
Derivative [Line Items]
Remaining Years to Maturity	9 years 69 days