Note 9 - Commitments and Contingencies - Changes in Product Liability Included in Accrued Liabilities (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Jun. 30, 2017
Beginning balance	$ 588,000	$ 291,000	$ 566,000
Warranties issued during the period	95,000	199,000	120,000
Settlements made during the period	(359,000)	(252,000)	(93,000)
Changes in liability for pre-existing warranties during the period	(33,000)	(52,000)	(5,000)
Ending balance	$ 291,000	$ 186,000	$ 588,000