Investments (Commercial Mortgage and Other Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 1,231,964	$ 1,211,215
Commercial mortgage loans, Percentage	100.00%	100.00%
Allowance for Credit Losses	$ (1,905)	$ (2,065)
Total commercial mortgage and other loans	1,230,059	1,209,150
Apartments and multi-family
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 376,650	$ 362,811
Commercial mortgage loans, Percentage	30.50%	29.90%
Hospitality
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 19,162	$ 16,083
Commercial mortgage loans, Percentage	1.60%	1.30%
Industrial
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 298,108	$ 263,999
Commercial mortgage loans, Percentage	24.20%	21.80%
Office
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 194,300	$ 187,450
Commercial mortgage loans, Percentage	15.80%	15.50%
Other
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 127,687	$ 131,961
Commercial mortgage loans, Percentage	10.40%	10.90%
Retail
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 193,474	$ 193,473
Commercial mortgage loans, Percentage	15.70%	16.00%
Commercial mortgage loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 1,209,381	$ 1,155,777
Commercial mortgage loans, Percentage	98.20%	95.40%
Agricultural property loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 22,583	$ 55,438
Commercial mortgage loans, Percentage	1.80%	4.60%