Investments (Mortgage Loans by Credit Quality Indicator) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [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%
Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 3,601,817	$ 2,953,180
1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	120,296	112,947
Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	61,094	70,637
0% - 59.99%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,925,755	$ 1,700,541
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	50.80%	54.20%
0% - 59.99% | Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,859,640	$ 1,621,056
0% - 59.99% | 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	64,749	77,118
0% - 59.99% | Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	1,366	2,367
60% - 69.99%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,292,466	$ 915,748
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	34.20%	29.20%
60% - 69.99% | Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 1,257,788	$ 881,611
60% - 69.99% | 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	34,678	14,332
60% - 69.99% | Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	0	19,805
70% - 79.99%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 415,330	$ 489,051
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	11.00%	15.60%
70% - 79.99% | Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 370,092	$ 446,565
70% - 79.99% | 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	20,869	7,947
70% - 79.99% | Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	24,369	34,539
Greater than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 149,656	$ 31,424
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	4.00%	1.00%
Greater than 80% | Greater than 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 114,297	$ 3,948
Greater than 80% | 1.00x - 1.20x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	0	13,550
Greater than 80% | Less than 1.00x
Financing Receivable, Recorded Investment [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 35,359	$ 13,926