Accumulated Other Comprehensive (Loss) Income, Reclassifications out of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	$ 0	$ 376	$ 249	$ 382
Salaries and employee benefits	7,834	8,272	24,479	23,876
Income taxes	5,535	6,532	18,418	20,875
Net income	10,616	10,714	32,058	33,533
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net income	(40)	127	76	274
Unrealized Gains (Losses) on Securities Available For Sale [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	0	376	249	382
Income taxes	0	(151)	(100)	(153)
Net income	0	225	149	229
Amortization of Pension and Postretirement Benefit Items [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	26	64	48	(29)
Net income	(40)	(98)	(73)	45
Amortization of Net Actuarial (Loss) Gain [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	(43)	77	(53)	223
Amortization of Prior Service (Cost) Credit [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	$ (23)	$ (239)	$ (68)	$ (149)