Investments (Mortgage Loans by Credit Quality Indicator) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 3,079,255	$ 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	$ 1,553,149	$ 1,326,199
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	50.50%	48.80%
Investment grade
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 1,405,901	$ 1,235,046
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	45.70%	45.40%
Average
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 81,284	$ 118,152
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	2.60%	4.40%
Watch list
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 22,036	$ 22,285
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	0.70%	0.80%
In or near default
Mortgage Loans on Real Estate [Line Items]
Mortgage loans, gross of valuation allowances	$ 16,885	$ 17,027
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	0.50%	0.60%