Accumulated Other Comprehensive Income Reclassification Out Of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gain on investment	$ 288	$ 83	$ 441	$ 186
Unrecognized loss	0	(2)	0	(4)
Income before Income Taxes	8,814	8,346	14,039	14,797
Tax	(1,894)	(2,672)	(2,946)	(4,657)
Net Income	6,920	5,674	11,093	10,140
Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net Income	0	53	0	110
Reclassification Out Of Accumulated Other Comprehensive Income | Unrealized Gains and Losses On Available-for-Sale Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gain on investment	0	83	0	173
Other-than-temporary impairments	0	0	0	0
Income before Income Taxes	0	83	0	173
Tax	0	(28)	0	(60)
Net Income	0	55	0	113
Reclassification Out Of Accumulated Other Comprehensive Income | Postretirement Benefits Plans
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Prior year service cost	0	0	0	0
Unrecognized loss	0	(2)	0	(4)
Income before Income Taxes	0	(2)	0	(4)
Tax	0	0	0	1
Net Income	$ 0	$ (2)	$ 0	$ (3)