Note 2 - Summary of Significant Accounting Policies - Cumulative Effect of Adjustments for New Accounting Pronouncements on Consolidated Balance Sheet (Details) - USD ($)		Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	[1]
Accrued liabilities		$ 5,258,000	$ 4,623,000	$ 4,605,000
Other noncurrent liabilities		305,000	132,000	327,000
Accumulated deficit		$ (129,589,000)	(105,404,000)	$ (105,581,000)
Accounting Standards Update 2014-09 [Member]
Accrued liabilities	[2]		18,000
Other noncurrent liabilities	[3]		(195,000)
Accumulated deficit	[4]		$ 177,000

[1] The condensed consolidated balance sheet as of December 31, 2017 has been derived from the audited consolidated financial statements as of that date.

[2] Change relates to future costs associated with extended warranties required to be recorded on adoption of ASC 606.

[3] Change relates to long-term deferred revenue related to the extended warranties not required to be recorded under ASC 606.

[4] Change relates to cumulative effect adjustment upon adoption of ASC 606.