Accumulated Other Comprehensive Income (Loss) (''AOCI'') - Amount Reclassified from AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Amount Reclassified from AOCI
Realized gains on sale of securities	$ (6)	$ 180
Interest income on taxable securities	2,877	2,774
Income tax expense	(3,934)	(3,726)
Net income	6,538	6,106
Unrealized Gains on Available-for-Sale Securities and I/O Strips
Amount Reclassified from AOCI
Net of tax	(4)	105
Unrealized Gains on Available-for-Sale Securities and I/O Strips | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Realized gains on sale of securities	(6)	180
Income tax expense	2	(75)
Net income	(4)	105
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity
Amount Reclassified from AOCI
Net of tax	8	8
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Interest income on taxable securities	13	14
Income tax expense	(5)	(6)
Net income	8	8
Defined Benefit Pension Plan Items
Amount Reclassified from AOCI
Net of tax	(30)	(28)
Defined Benefit Pension Plan Items | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Income before income tax	(51)	(47)
Income tax benefit	21	19
Net of tax	(30)	(28)
Prior transition obligation | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Income before income tax	18	13
Actuarial losses | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Income before income tax	(69)	(60)
Accumulated Other Comprehensive Income / (Loss)
Amount Reclassified from AOCI
Net of tax	(26)	85
Accumulated Other Comprehensive Income / (Loss) | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Net of tax	$ (26)	$ 85