Income Taxes (Sources of Difference and Tax Effects) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Sources of the difference and the tax effects
Federal income tax expense (benefit), at statutory rate	$ 25,973	$ 21,893	$ 30,345
Tax-exempt investment income, net	(1,626)	(1,862)	(4,123)
State taxes, net	34	85	19
Nondeductible expenses	488	494	237
Remeasurement of deferred tax liability upon enactment of the TCJA			(1,540)
Tax windfall related to share-based stock compensation	(1,003)	(79)	(333)
Other, net	214	525	(292)
Total income tax expense (benefit)	$ 24,080	$ 21,056	$ 24,313