Investments (Mortgage Loans by Maturity Date) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 3,175,654	$ 2,718,709
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	$ 932,955	$ 860,362
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	29.40%	31.60%
Due after five years through ten years
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 1,511,275	$ 1,165,530
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	47.60%	42.90%
Due after ten years
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 731,424	$ 692,817
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	23.00%	25.50%