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	$ 1,337,506	$ 1,356,374
Commercial mortgage loans, Percentage	100.00%	100.00%
Allowance for credit losses	$ (2,300)	$ (2,896)
Total commercial mortgage and other loans	1,335,206	1,353,478
Apartments and multi-family
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 264,146	$ 304,644
Commercial mortgage loans, Percentage	19.80%	22.40%
Hospitality
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 5,618	$ 3,633
Commercial mortgage loans, Percentage	0.40%	0.30%
Industrial
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 438,973	$ 355,758
Commercial mortgage loans, Percentage	32.80%	26.20%
Office
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 315,647	$ 305,537
Commercial mortgage loans, Percentage	23.60%	22.50%
Other
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 128,779	$ 137,781
Commercial mortgage loans, Percentage	9.60%	10.20%
Retail
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 123,138	$ 194,646
Commercial mortgage loans, Percentage	9.20%	14.40%
Commercial Mortgage Loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 1,276,301	$ 1,301,999
Commercial mortgage loans, Percentage	95.40%	96.00%
Agricultural property loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 61,205	$ 54,375
Commercial mortgage loans, Percentage	4.60%	4.00%