Accumulated Other Comprehensive Income (Loss), Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net gain on securities transactions	[1]	$ 0		$ 0		$ 0	$ 1,155
Salaries and employee benefits		12,403		11,648		24,828	23,021
Income tax effect		4,937		3,921		9,704	8,227
Net income		14,433	$ 14,083	11,254	$ 13,313	28,516	24,567
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net income		50		141		257	1,155
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		0		0		0	1,155
Income tax effect		0		0		0	(300)
Net income		0		0		0	855
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 effect		(17)		(51)		(90)	(107)
Net income		50		141		257	300
Amortization of Net Actuarial Gain [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Salaries and employee benefits		169		143		397	309
Amortization of Prior Service (Cost) Credit [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Salaries and employee benefits		$ (102)		$ 49		$ (50)	$ 98

[1] Not within the scope of ASC 606.