Income Taxes (Sources of Difference and Tax Effects) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sources of the difference and the tax effects
Federal income tax expense (benefit), at statutory rate	$ 32,649	$ (10,025)	$ 29,162
Tax-exempt investment income, net	(4,194)	(4,889)	(5,429)
State taxes, net	58	26	115
Nondeductible expenses	202	233	222
Other, net	(18)	(137)	(106)
Total income tax expense (benefit)	$ 28,697	$ (14,792)	$ 23,964