Investments Investments (Transfers) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	$ 5,406,898
Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	5,457,290
Mortgage Loans on Real Estate [Member] | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	1,009,454
Mortgage Loans on Real Estate [Member] | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	1,021,661
Short-term Investments [Member] | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	101,428
Short-term Investments [Member] | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	101,338
Cash and Cash Equivalents [Member] | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	501,593
Cash and Cash Equivalents [Member] | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	501,593
Accrued Interest [Member] | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	43,739
Accrued Interest [Member] | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	43,739
Fixed Maturities [Member] | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	3,750,684
Fixed Maturities [Member] | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	3,788,959
Fixed Maturities [Member] | Corporate securities | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	2,585,095
Fixed Maturities [Member] | Corporate securities | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	2,606,816
Fixed Maturities [Member] | Asset-backed securities | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	137,251
Fixed Maturities [Member] | Asset-backed securities | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	138,918
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	703,313
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	704,065
Fixed Maturities [Member] | US Government Agencies Debt Securities [Member] | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	240,952
Fixed Maturities [Member] | US Government Agencies Debt Securities [Member] | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	256,168
Fixed Maturities [Member] | State and political subdivisions | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	27,297
Fixed Maturities [Member] | State and political subdivisions | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	27,555
Fixed Maturities [Member] | Other foreign government, supranational and foreign government-sponsored enterprises | Reported Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	56,776
Fixed Maturities [Member] | Other foreign government, supranational and foreign government-sponsored enterprises | Estimate of Fair Value Measurement [Member]
Transfer To Investments [Line Items]
Transfer to Investments	$ 55,437