Note 9 - Defined Benefit Plans (Details Textual) - USD ($)	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2018
Payment for Pension and Other Postretirement Benefits, Total	$ 24,000
Defined Benefit Plan Required Contributions in Current Fiscal Year	$ 0
Scenario, Forecast [Member]
Payment for Pension and Other Postretirement Benefits, Total		$ 60,000

Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3536-108585

Name:	us-gaap_PensionAndOtherPostretirementBenefitContributions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration