Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	$ 26,674	$ 34,421	$ 26,674	$ 29,672	$ 23,526
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax	17,539	40,690	17,539	(20,116)	(2,928)
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(454)	(698)	(454)	0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(9,589)	5,571	(9,589)	(49,788)	(26,454)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax		8,675	(1,511)	4,046
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, after Tax		25,747	37,322	(17,586)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax		(244)	(454)	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		16,828	38,379	(21,632)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax		928	1,487	1,075
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		2,596	(333)	(2,024)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax		0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1,668	(1,820)	(3,099)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		7,747	(2,998)	2,971
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax		23,151	37,655	(15,562)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax		(244)	(454)
Other Comprehensive Income (Loss), Net of Tax		15,160	40,199	(18,533)
Debt Securities, Held-to-maturity, Transfer, Amount			373,900
Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, before Tax	$ 24,200
Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, Net of Tax		0	19,095	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax		1,175	1,882	1,361
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		1,175	1,882	1,361
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		247	395	286
Gain (Loss) on Sale of Investments		3,286	(421)	(2,271)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax		(3,286)	421	2,562
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax		(690)	88	538
Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax					(995)
Accumulated Other Comprehensive Income (Loss), Net of Tax					(995)
Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax					3,175
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax					(631)
Accumulated Other Comprehensive Income (Loss), Net of Tax					(3,806)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gain (Loss) on Sale of Investments		3,286	(421)	(2,562)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax				(2,024)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		$ (2,596)	$ 333	$ 2,024
Adjustments for New Accounting Pronouncement [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax					23,526
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax					(3,923)
Accumulated Other Comprehensive Income (Loss), Net of Tax					$ (27,449)