Note 7 - Retirement Plans (Details Textual) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)
Pension Plan [Member] \| Gray Pension Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 3	$ 3
Profit Sharing Contribution [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	3	3
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 3	$ 10

Amount of contribution expected to be received by defined benefit plan from employer in remainder of current fiscal year. Excludes contribution previously paid by employer in current fiscal year.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921

Name:	us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsRemainderOfFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant