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	$ 1,319,007	$ 1,356,374
Commercial mortgage loans, Percentage	100.00%	100.00%
Allowance for credit losses	$ (2,396)	$ (2,896)
Total commercial mortgage and other loans	1,316,611	1,353,478
Apartments and multi-family
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 284,999	$ 304,644
Commercial mortgage loans, Percentage	21.60%	22.40%
Hospitality
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 4,787	$ 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	$ 390,931	$ 355,758
Commercial mortgage loans, Percentage	29.60%	26.20%
Office
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 286,659	$ 305,537
Commercial mortgage loans, Percentage	21.70%	22.50%
Other
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 138,177	$ 137,781
Commercial mortgage loans, Percentage	10.50%	10.20%
Retail
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 160,506	$ 194,646
Commercial mortgage loans, Percentage	12.20%	14.40%
Commercial Mortgage Loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 1,266,059	$ 1,301,999
Commercial mortgage loans, Percentage	96.00%	96.00%
Agricultural property loans
Commercial Mortgage and Other Loans [Line Items]
Commercial mortgage and agricultural property loans by property type	$ 52,948	$ 54,375
Commercial mortgage loans, Percentage	4.00%	4.00%