Investments (Mortgage Loans by Maturity Date) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 2,496,251	$ 2,312,167
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	100.00%	100.00%
Due within five years
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	1,024,065	1,187,387
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	41.00%	51.30%
Due after five years through ten years
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	963,479	776,655
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	38.60%	33.60%
Due after ten years
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 508,707	$ 348,125
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	20.40%	15.10%