Investments (Mortgage Loans by Maturity Date) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,299,320	$ 3,136,764
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]
Loans Receivable, Gross, Commercial, Real Estate	$ 844,192	$ 873,280
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	25.60%	27.80%
Due after five years through ten years
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,709,137	$ 1,561,535
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	51.80%	49.80%
Due after ten years
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 745,991	$ 701,949
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	22.60%	22.40%