Investments (Mortgage Loans by Maturity Date) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,614,446	$ 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	$ 793,736	$ 873,280
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	22.00%	27.80%
Due after five years through ten years
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,952,001	$ 1,561,535
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	54.00%	49.80%
Due after ten years
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 868,709	$ 701,949
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	24.00%	22.40%