Accumulated Other Comprehensive Income ("AOCI") - Reclassifications Out of AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains (losses), net	$ 812	$ 836	$ 867
Income taxes	(10,826)	(7,007)	(6,020)
Net Income	15,249	16,301	15,039
Reclassification of stranded tax effects from tax rate change	(545)
Total reclassifications	528	543	564
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification of stranded tax effects from tax rate change	141	0	0
Total reclassifications	1,073	543	564
Realized gain on sale of securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification of stranded tax effects from tax rate change	(141)
Total reclassifications	528	543	564
Realized gain on sale of securities | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains (losses), net	812	836	867
Income taxes	(284)	(293)	(303)
Net Income	528	543	564
Adjustments Related to Pension Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification of stranded tax effects from tax rate change	(404)
Adjustments Related to Pension Benefits | Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	$ 404	$ 0	$ 0