Note 5 - Components of Pension and Other Post-employment Benefit (OPEB) Plans Net Periodic Benefit Costs - Components of Net Periodic Benefit (Credit) Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Plan [Member]
Service Cost	$ 296	$ 987	$ 887	$ 2,963
Interest Cost	5,044	6,275	15,132	18,825
Expected Return on Plan Assets	(10,455)	(10,114)	(31,365)	(30,343)
Amortization of Prior Service Credits	0	(92)	0	(275)
Amortization of Actuarial Loss	1,730	1,490	5,191	4,469
Net Periodic Benefit (Credit) Cost	(3,385)	(1,454)	(10,155)	(4,361)
Other Postretirement Benefits Plan [Member]
Service Cost	0	0	0	0
Interest Cost	3,199	4,580	9,597	13,740
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credits	(601)	(601)	(1,804)	(1,804)
Amortization of Actuarial Loss	2,319	2,315	6,958	6,946
Net Periodic Benefit (Credit) Cost	$ 4,917	$ 6,294	$ 14,751	$ 18,882