Investments (Mortgage Loans by Credit Quality Indicator) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Credit Quality Indicators [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%
High investment grade
Credit Quality Indicators [Line Items]
Mortgage loans, gross of valuation allowances	1,556,974	1,235,605
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	62.40%	53.50%
Investment grade
Credit Quality Indicators [Line Items]
Mortgage loans, gross of valuation allowances	754,369	834,494
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	30.20%	36.10%
Average
Credit Quality Indicators [Line Items]
Mortgage loans, gross of valuation allowances	106,912	132,607
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	4.30%	5.70%
Watch list
Credit Quality Indicators [Line Items]
Mortgage loans, gross of valuation allowances	49,173	76,463
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	2.00%	3.30%
In or near default
Credit Quality Indicators [Line Items]
Mortgage loans, gross of valuation allowances	$ 28,823	$ 32,998
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	1.10%	1.40%