Accumulated Other Comprehensive Income (Loss), Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net gain on securities transactions	[1]	$ 0	$ 1,155
Salaries and employee benefits		12,425	11,373
Income tax effect		4,767	4,306
Net income		14,083	13,313
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Net income		207	159
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	1,155
Income tax effect		0	(300)
Net income		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		(73)	(56)
Net income		207	159
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		228	166
Amortization of Prior Service Credit [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Abstract]
Salaries and employee benefits		$ 52	$ 49

[1] Not within the scope of ASC 606.