Note 1 - Nature of Business (Details Textual)				3 Months Ended	12 Months Ended
	Nov. 02, 2017 USD ($)	Feb. 17, 2016 USD ($)	Jan. 25, 2016 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Number of Reportable Segments					1
Debt Issuance Costs, Net, Total		$ 15,000
Write off of Deferred Debt Issuance Cost		140,000
Long-term Debt, Total					$ 74,562,000
Consortium of Banks Led By CoBank ABC [Member]
Debt Instrument, Term	5 years
Debt Issuance Costs, Net, Total	$ 28,000
Write off of Deferred Debt Issuance Cost	3,700,000
Debt Agreement, Maximum Borrowing Capacity	92,000,000
Revolving Credit Facility [Member]
Debt Instrument, Term			5 years
Line of Credit Facility, Maximum Borrowing Capacity			$ 5,000,000
Revolving Credit Facility [Member] | Consortium of Banks Led By CoBank ABC [Member]
Line of Credit Facility, Maximum Borrowing Capacity	5,000,000
Term Loan Facility [Member] | Consortium of Banks Led By CoBank ABC [Member]
Long-term Debt, Total	87,000,000
Line of Credit, Accordion Feature	$ 20,000,000
Senior Notes [Member]
Debt Instrument, Term			5 years
Debt Instrument, Face Amount			$ 85,000,000
Proceeds from Issuance of Debt		85,000,000
Debt Instrument, Periodic Payment, Total		1,000,000
Write off of Deferred Debt Issuance Cost						$ 3,070,000
Payments of Debt Restructuring Costs				$ 77,900
Capital Expenditure Limit					$ 7,500,000	8,500,000
Subordinated Debt [Member]
Debt Instrument, Term			5 years 182 days
Debt Instrument, Face Amount		15,300,000	$ 15,000,000
Proceeds from Issuance of Debt		$ 15,300,000
Write off of Deferred Debt Issuance Cost						$ 621,000