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Note 11 - Pension Plan and Other Postretirement Benefits - Pension Fund Assets Measured at Fair Value and NAV (Details) - Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value of Plan Assets	$ 329,781	$ 269,783	$ 285,319
NAV Practical Expedient to Fair Valuation [Member] | Other - SEI Energy Debt Collective Fund [Member] | SEI Energy Debt Collective Fund [Member]
Fair Value of Plan Assets	9,540	11,476
Fair Value, Inputs, Level 1 [Member]
Fair Value of Plan Assets	$ 320,241	$ 258,307

X

- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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