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Note 11 - Pension Plan and Other Postretirement Benefits - Weighted-average Assumptions Used to Determine Benefit Obligations (Details)	Dec. 31, 2019	Dec. 31, 2018
Pension Plan [Member]
Discount Rate	3.47%	4.50%
Pension Plan [Member] | Participants to Age 39 [Member]
Rate of Increase in Future Compensation Level	4.50%	4.50%
Pension Plan [Member] | Participants Age 40 to 49 [Member]
Rate of Increase in Future Compensation Level	3.50%	3.50%
Pension Plan [Member] | Participants Age 50 and Older [Member]
Rate of Increase in Future Compensation Level	2.75%	2.75%
Executive Survivor and Supplemental Retirement Plan [Member]
Discount Rate	3.36%	4.46%
Rate of Increase in Future Compensation Level	3.50%	3.40%
Other Postretirement Benefits Plan [Member]
Discount Rate	3.43%	4.44%

X

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

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X

- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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