Note 13 - Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance	$ 1,713,785	$ 1,696,534	$ 1,690,426
Change, net of tax	4,433	4,421	5,159
Balance	1,760,787	1,713,785	1,696,534
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Balance	(13)	(13)	(13)
Change, net of tax	0	0	0
Balance	(13)	(13)	(13)
Balance, tax	0	0	0
Change, tax	0	0	0
Balance, tax	0	0	0
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Balance	7,632	(348)	(8,784)
Change, net of tax	(12,307)	7,980	8,436
Balance	(4,675)	7,632	(348)
Balance, tax	0	0	0
Change, tax	4,689	0	0
Balance, tax	4,689	0	0
Accumulated Defined Benefit Plans Adjustment, Net Transition Attributable to Parent [Member]
Balance	(40,508)	(36,949)	(33,672)
Change, net of tax	16,740	(3,559)	(3,277)
Balance	(23,768)	(40,508)	(36,949)
Balance, tax	12,575	12,575	12,575
Change, tax	(6,379)	0	0
Balance, tax	6,196	12,575	12,575
AOCI Attributable to Parent [Member]
Balance	(32,889)	(37,310)	(42,469)
Change, net of tax	4,433	4,421	5,159
Balance	(28,456)	(32,889)	(37,310)
Balance, tax	12,575	12,575	12,575
Change, tax	(1,690)	0	0
Balance, tax	$ 10,885	$ 12,575	$ 12,575