Note 9 - Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($)		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Settlement loss		$ (2,300,000)	$ (4,600,000)	$ 0
Pension Plan [Member]
Service cost		2,662,000	2,709,000	2,204,000
Interest cost		1,729,000	1,937,000	2,454,000
Expected return on plan assets		(3,610,000)	(3,900,000)	(3,561,000)
Recognized actuarial loss		1,904,000	2,160,000	1,726,000
Settlement loss		2,304,000	4,583,000	0
Net periodic benefit cost (gain)	[1]	4,989,000	7,489,000	2,823,000
Net (gain) loss		(2,879,000)	2,704,000	3,034,000
Total expense recognized in net periodic benefit cost and other comprehensive income		2,110,000	10,193,000	5,857,000
Postemployment Retirement Benefits [Member]
Service cost		1,462,000	1,372,000	1,083,000
Interest cost		654,000	778,000	941,000
Recognized actuarial loss		580,000	306,000	27,000
Net periodic benefit cost (gain)		1,566,000	1,327,000	922,000
Net (gain) loss		(863,000)	3,762,000	3,749,000
Total expense recognized in net periodic benefit cost and other comprehensive income		703,000	5,089,000	4,671,000
Prior service cost recognition		$ (1,130,000)	$ (1,129,000)	$ (1,129,000)

[1] The components of net periodic benefit cost other than the service cost component are included in Other income (expense), net in the Consolidated Statements of Income.