Retirement Plans, Amounts Recognized in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Pension Plan [Member]
Amounts recognized in accumulated other comprehensive income [Abstract]
Net actuarial loss (gain)	$ 81,376	$ 52,160
Prior service cost (credit)	0	0
Accumulated other compensation income	81,376	52,160
SERP [Member]
Amounts recognized in accumulated other comprehensive income [Abstract]
Net actuarial loss (gain)	480	460
Prior service cost (credit)	0	0
Accumulated other compensation income	480	460
Other Postretirement Benefits [Member]
Amounts recognized in accumulated other comprehensive income [Abstract]
Net actuarial loss (gain)	(3,189)	(3,795)
Prior service cost (credit)	0	0
Accumulated other compensation income	$ (3,189)	$ (3,795)

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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- Definition

Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
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- Definition

Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

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