Investments (Mortgage Loans by Property Type) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,783,207	$ 3,136,764
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	100.00%	100.00%
Office Building [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,270,113	$ 980,858
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	33.60%	31.30%
Retail Site [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,179,936	$ 1,026,018
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	31.20%	32.70%
Industrial Property [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 713,461	$ 527,485
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	18.80%	16.80%
Apartment Building [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 447,088	$ 420,014
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	11.80%	13.40%
Other Property [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 172,609	$ 182,389
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	4.60%	5.80%