Cosolidated Statements of Comprehensive Income (parentheticals) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
(Tax) benefit on benefit plan liability adjustments - net gain (loss)	$ 191	$ 1,886	$ (660)
(Tax) benefit on benefit plan liability adjustments - prior service costs	0	2	0
(Tax) benefit on reclassification adjustment of benefit plan liability - net loss	(958)	434	(586)
(Tax) benefit on reclassification adjustment of benefit plan liability - prior service cost	23	19	43
Interest Rate Swap
Tax (benefit) on reclassification of net realized (gains) losses on settled/amortized derivatives	(287)	(666)	(599)
Commodity Contract
Tax (benefit) on reclassification of net realized (gains) losses on settled/amortized derivatives	(96)	55	(31)
(Tax) benefit on net unrealized gains (losses) on commodity derivatives	$ 14	$ 126	$ (228)

Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

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Amount of tax (expense) benefit 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).

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount of tax (expense) benefit for reclassification adjustment from accumulated other comprehensive (income) loss of defined benefit plan.

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Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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