Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	$ 26,674	$ 26,674	$ 29,672	$ 23,526	$ 14,740
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax	17,539	17,539	(20,116)	(2,928)	(3,005)
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(454)	(454)	0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(9,589)	(9,589)	(49,788)	(26,454)	$ (17,745)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax		(1,511)	4,046	9,241
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, after Tax		37,322	(17,586)	1,261
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax		(454)	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		38,379	(21,632)	(7,980)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax		1,487	1,075	455
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		(333)	(2,024)	1,184
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax		0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(1,820)	(3,099)	(729)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		(2,998)	2,971	8,786
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax		37,655	(15,562)	77
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax		(454)
Other Comprehensive Income (Loss), Net of Tax		40,199	(18,533)	(8,709)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				(995)
Debt Securities, Held-to-maturity, Transfer, Amount		373,900	0	0
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		19,095	0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax		1,882	1,361	576
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		1,882	1,361	576
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		395	286	121
Gain (Loss) on Sale of Investments		(421)	(2,271)	1,821
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax		421	2,562	(1,821)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax		88	538	(637)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gain (Loss) on Sale of Investments		(421)	(2,562)	1,821
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax		40,199	(18,533)	(8,709)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				(3,806)
Pension Plan [Member] | AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				(3,175)
Debt 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				(1,184)
Debt Securities [Member] | AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				(631)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		$ 333	$ 2,024	(1,184)
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)