Investments (Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	$ 1,558	$ 2,651
Addition to (release of) allowance for losses	236	(1,093)
Charge-offs, net of recoveries	0	0
Total Ending Balance	1,794	1,558
Commercial mortgage loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	1,513	2,587
Addition to (release of) allowance for losses	215	(1,074)
Charge-offs, net of recoveries	0	0
Total Ending Balance	1,728	1,513
Agricultural Property Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	45	64
Addition to (release of) allowance for losses	21	(19)
Charge-offs, net of recoveries	0	0
Total Ending Balance	$ 66	$ 45