Investments (Commercial Mortgage and Other Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 1,227,627	$ 1,211,215
Commercial mortgage loans, Percentage	100.00%	100.00%
Allowance for Credit Losses	$ (1,959)	$ (2,065)
Total commercial mortgage and other loans	1,225,668	1,209,150
Apartments and multi-family
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 355,719	$ 362,811
Commercial mortgage loans, Percentage	29.00%	29.90%
Hospitality
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 15,853	$ 16,083
Commercial mortgage loans, Percentage	1.30%	1.30%
Industrial
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 286,521	$ 263,999
Commercial mortgage loans, Percentage	23.20%	21.80%
Office
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 197,159	$ 187,450
Commercial mortgage loans, Percentage	16.10%	15.50%
Other
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 129,617	$ 131,961
Commercial mortgage loans, Percentage	10.60%	10.90%
Retail
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 189,040	$ 193,473
Commercial mortgage loans, Percentage	15.40%	16.00%
Commercial mortgage loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 1,173,909	$ 1,155,777
Commercial mortgage loans, Percentage	95.60%	95.40%
Agricultural property loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 53,718	$ 55,438
Commercial mortgage loans, Percentage	4.40%	4.60%