Derivative Instruments (Exposure from Credit Derivatives by Rating of the Underlying Credits) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	$ 7,958	[1]	$ 8,565	[1]
Maximum Potential Future Exposure on Credit Risk Derivatives	645,700	[1],[2]	664,700	[1],[2]
Derivative Average Remaining Maturity	5 years 1 month	[1],[3]	4 years 5 months	[1],[3]
Standard Poors AAA To A Minus Ratings [Member] | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	1,059	[1]	614	[1]
Maximum Potential Future Exposure on Credit Risk Derivatives	112,500	[1],[2]	117,500	[1],[2]
Derivative Average Remaining Maturity	5 years	[1],[3]	5 years 1 month	[1],[3]
Standard Poors AAA To A Minus Ratings [Member] | Credit Default Swaps Referencing Indices [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	0	[1]	0	[1]
Maximum Potential Future Exposure on Credit Risk Derivatives	0	[1],[2]	0	[1],[2]
Standard Poors AAA To A Minus Ratings [Member] | Credit Default Subtotal [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	1,059	[1]	614	[1]
Maximum Potential Future Exposure on Credit Risk Derivatives	112,500	[1],[2]	117,500	[1],[2]
Derivative Average Remaining Maturity	5 years	[1],[3]	5 years 1 month	[1],[3]
Standard Poors BBB Rating [Member] | Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	608	[1]	656	[1]
Maximum Potential Future Exposure on Credit Risk Derivatives	127,200	[1],[2]	142,200	[1],[2]
Derivative Average Remaining Maturity	5 years	[1],[3]	4 years 11 months	[1],[3]
Standard Poors BBB Rating [Member] | Credit Default Swaps Referencing Indices [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	6,291	[1]	7,295	[1]
Maximum Potential Future Exposure on Credit Risk Derivatives	406,000	[1],[2]	405,000	[1],[2]
Derivative Average Remaining Maturity	5 years 2 months	[1],[3]	5 years	[1],[3]
Standard Poors BBB Rating [Member] | Credit Default Subtotal [Member]
Credit Derivatives [Line Items]
Credit Derivative Current Fair Value	6,899	[1]	7,951	[1]
Maximum Potential Future Exposure on Credit Risk Derivatives	$ 533,200	[1],[2]	$ 547,200	[1],[2]
Derivative Average Remaining Maturity	5 years 2 months	[1],[3]	5 years	[1],[3]

[1] The rating agency designations are based on ratings from Standard and Poor’s (“S&P”).

[2] Assumes the value of the referenced credit obligations is zero.

[3] The weighted average years to maturity of the credit default swaps is calculated based on weighted average notional amounts.