Note 4 - Periodic Pension Expense (Details Textual) - Forecast [Member] - Noncontributory Qualified Defined Pension Plans [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended
Apr. 30, 2021	Jun. 30, 2021
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	$ 13.7
Minimum [Member]
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits		$ 7.5
Maximum [Member]
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits		$ 8.5

Amount of payment, which decreases benefit obligation of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract. Excludes decreases to benefit obligation for remeasurement due to settlement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration