Note 13 - Retirement Benefit Plans - Assumed Healthcare Trend Rates (Details) - Postretirement Health Coverage [Member]	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.50%	5.00%
Year that the rate reaches the ultimate trend rate	2037	2032
Pre-65 [Member]
Healthcare cost trend rate assumption for the next year	5.90%	6.22%
Post-65 [Member]
Healthcare cost trend rate assumption for the next year	6.20%	6.22%

Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

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Year ultimate health care cost trend rate is expected to be reached, in CCYY format.

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