Investments (Mortgage Loans by Credit Quality Indicator) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,879,769	$ 3,783,207
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	100.00%	100.00%
Mortgage Loans By Credit Quality Indicator Range Four [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 138,917	$ 149,656
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	3.60%	4.00%
Mortgage Loans By Credit Quality Indicator Range Three [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 413,445	$ 415,330
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	10.70%	11.00%
Mortgage Loans By Credit Quality Indicator Range Two [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,294,234	$ 1,292,466
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	33.40%	34.20%
Mortgage Loans By Credit Quality Indicator Range One [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 2,033,173	$ 1,925,755
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	52.30%	50.80%
Debt Service Coverage Ratio Range Three [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 60,411	$ 61,094
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	35,021	35,359
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	24,207	24,369
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	0	0
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	1,183	1,366
Debt Service Coverage Ratio Range Two [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	119,859	120,296
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	0	0
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	20,734	20,869
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	34,584	34,678
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	64,541	64,749
Debt Service Coverage Ratio Range One [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	3,699,499	3,601,817
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	103,896	114,297
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	368,504	370,092
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	1,259,650	1,257,788
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,967,449	$ 1,859,640