Investments (Mortgage Loans by Credit Quality Indicator) (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%
High investment grade
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 1,681,552	$ 1,326,199
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	52.90%	48.80%
Investment grade
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 1,378,194	$ 1,235,046
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	43.40%	45.40%
Average
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 77,217	$ 118,152
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	2.40%	4.40%
Watch list
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 17,857	$ 22,285
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	0.60%	0.80%
In or near default
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 20,834	$ 17,027
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	0.70%	0.60%