Accumulated Other Comprehensive Income (Loss), Reclassifications out of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	$ 0	$ 0	$ 668	$ 249
Salaries and employee benefits	8,995	7,834	26,932	24,479
Income taxes	6,667	5,535	19,033	18,418
Net income	10,930	10,616	31,803	32,058
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net income	(8)	(40)	376	76
Net Unrealized Holding Gain (Loss) 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	668	249
Income taxes	0	0	(267)	(100)
Net income	0	0	401	149
Net Change in Net Actuarial Loss and Prior Service Credit on Pension and Postretirement Benefit Plans, Net of Tax [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	6	26	17	48
Net income	(8)	(40)	(25)	(73)
Amortization of Net Actuarial Loss [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	8	(43)	25	(53)
Amortization of Prior Service Cost [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	$ (22)	$ (23)	$ (67)	$ (68)