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, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 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		11,909			10,899			36,737	33,920
Income tax effect		5,523			4,761			15,227	12,988
Net income		16,762	$ 14,433	$ 14,083	14,071	$ 11,254	$ 13,313	45,278	38,638
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net income		(30)			201			227	1,356
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		10			(70)			(80)	(177)
Net income		(30)			201			227	501
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		137			222			534	531
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		$ (177)			$ 49			$ (227)	$ 147

[1] Not within the scope of ASC 606.