Note 8 - Accrued Retirement Benefits - Accrued Retirement Benefits (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued retirement benefits	$ 9,742	$ 9,867
Less current portion	(165)	(165)
Non-current portion of accrued retirement benefits	9,577	9,702
Pension Plan [Member] \| Qualified Plan [Member]
Accrued retirement benefits	7,547	7,658
Supplemental Employee Retirement Plan [Member] \| Nonqualified Plan [Member]
Accrued retirement benefits	$ 2,195	$ 2,209

Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Section 45
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant