Other Comprehensive (Loss) Income, Reclassifications out of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	$ 0	$ 0	$ 249	$ 6
Salaries and employee benefits	8,164	8,012	16,645	15,604
Income taxes	6,467	7,240	12,883	14,343
Net income	10,727	11,808	21,442	22,819
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net income	(49)	71	116	147
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	0	249	6
Income taxes	0	0	(100)	(2)
Net income	0	0	149	4
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	33	(48)	22	(93)
Net income	(49)	71	(33)	143
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	(15)	74	(10)	146
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	$ (67)	$ 45	$ (45)	$ 90