Accumulated Other Comprehensive Income (Loss), Reclassifications out of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net gain on securities transactions	[1]	$ 1,155	$ 0
Salaries and employee benefits		11,373	11,451
Income tax (benefit) expense		4,306	4,644
Net income		13,313	14,558
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net income		159	98
Unrealized Gains on Securities Available for Sale [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net gain on securities transactions		1,155	0
Income tax (benefit) expense		(300)	0
Net income		855	0
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 [Abstract]
Income tax (benefit) expense		(56)	(35)
Net income		159	98
Amortization of Net Actuarial Gain (Loss) [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Salaries and employee benefits		166	48
Amortization of Prior Service Cost [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Salaries and employee benefits		$ 49	$ 85

[1] Not within the scope of ASC 606.