Accumulated Other Comprehensive Income Reclassification Out Of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gain on investment	$ 153	$ 103
Unrecognized loss	0	(2)
Income before Income Taxes	5,225	6,451
Tax	(1,052)	(1,985)
Net Income	4,173	4,466
Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net Income	0	57
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	90
Other-than-temporary impairments	0	0
Income before Income Taxes	0	90
Tax	0	(32)
Net Income	0	58
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
Unrecognized loss	0	(2)
Income before Income Taxes	0	(2)
Tax	0	1
Net Income	$ 0	$ (1)