Investments (Mortgage Loans by Portfolio Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Company-held mortgage loans held-for-investment, net
Commercial	$ 281,552	$ 286,002
Percentage of loans receivable on commercial mortgage loans	69.10%	70.40%
Agricultural	$ 127,610	$ 121,858
Percentage of loans receivable on agricultural mortgage loans	31.30%	30.00%
Subtotal	$ 409,162	$ 407,860
Percentage of loans receivable on subtotal	100.40%	100.40%
Valuation allowances	$ (1,772)	$ (1,775)	$ (720)	$ (640)
Percentage of loans receivable on valuation allowances	(0.40%)	(0.40%)
Total mortgage loans, net	$ 407,390	$ 406,085
Percentage Of Mortgage Loans On Real Estate Commercial And Consumer Net To Mortgage Loans On Real Estate Commercial And Consumer Net	100.00%	100.00%