Note 12 - Commitments and Contingencies (Details Textual) - USD ($)	1 Months Ended		3 Months Ended	12 Months Ended
	Nov. 30, 2016	Jun. 30, 2015	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Leases, Rent Expense, Total				$ 849,000	$ 804,000
Self-insured Amount per Individual Claim		$ 50,000
Self-insured, Maximum Coverage Policy		$ 1,800,000
Self Insurance Reserve				60,000	102,000
Workers' Compensation, Maximum Coverage Policy				1,800,000
Workers' Compensation, Accumulated Payments on Claims				1,800,000
Workers' Compensation, Estimated Accruals			$ 267,000	1,600,000
Other Noncurrent Assets [Member]
Worker's Compensation, Prepaid Amount				$ 189,000
Sales Agreement with HydroFLOW USA [Member]
Licencing Agreement, Royalties on Gross Revenues Payable, Percentage						3.50%
Purchase Commitment, Minimum Amount Committed Per Year						$ 655,000
Purchase Commitment, Current Period Obligation Payment Allocated to Following Fiscal Year	$ 220,000
Purchase Commitment, Minimum Amount Committed, Next Twelve Months						875,000
Purchase Commitment, Amount Ordered					280,000
Accrued Royalties					$ 0	$ 0