Note 2 - Summary of Significant Accounting Policies - Impact of New Standard on Consolidated Balance Sheet and Consolidated Statements of Operations (Details) - USD ($)		3 Months Ended			6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017	[1]
Revenue		$ 5,525,000		$ 3,076,000	$ 9,224,000	$ 6,117,000
Cost of revenue		2,711,000		1,837,000	5,063,000	3,456,000
Gross profit		2,814,000		1,239,000	4,161,000	2,661,000
Loss from operations		(10,295,000)		(9,063,000)	(21,635,000)	(15,479,000)
Comprehensive and net loss		$ (11,516,000)		$ (10,425,000)	$ (24,185,000)	$ (17,120,000)
Basic and diluted (in dollars per share)		$ (0.37)		$ (0.54)	$ (0.85)	$ (1.10)
Accrued liabilities		$ 5,258,000			$ 5,258,000		$ 4,623,000	$ 4,605,000
Other noncurrent liabilities		305,000			305,000		132,000	327,000
Accumulated deficit		(129,589,000)			(129,589,000)		(105,404,000)	$ (105,581,000)
Accounting Standards Update 2014-09 [Member]
Gross profit					315,000
Accrued liabilities	[2]						18,000
Other noncurrent liabilities	[3]						(195,000)
Accumulated deficit	[4]						$ 177,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue		5,405,000			8,894,000
Cost of revenue		2,705,000			5,048,000
Gross profit		2,700,000			3,846,000
Loss from operations		(10,409,000)			(21,950,000)
Comprehensive and net loss		$ (11,630,000)			$ (24,500,000)
Basic and diluted (in dollars per share)		$ (0.37)			$ (0.86)
Accrued liabilities		$ 5,302,000			$ 5,302,000
Other noncurrent liabilities		753,000			753,000
Accumulated deficit		(130,081,000)			(130,081,000)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue		120,000	[5]		330,000
Cost of revenue		6,000	[6]		15,000
Gross profit		114,000	[7]		315,000
Loss from operations		114,000	[7]		315,000
Comprehensive and net loss		$ 114,000	[7]		$ 315,000
Basic and diluted (in dollars per share)			[7]		$ 0.01
Accrued liabilities	[8]	$ 44,000			$ 44,000
Other noncurrent liabilities	[9]	448,000			448,000
Accumulated deficit	[10]	$ (492,000)			$ (492,000)

[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.

[5] Change relates to revenue from extended assurance warranties for which no deferral is required on the adoption of ASC 606.

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

[7] Change relates to the net gain adjustment on the adoption of ASC 606.

[8] Change relates to future costs associated with extended warranties required to be recorded on the adoption of ASC 606, partially offset by the current portion of deferred revenue in connection with the extended warranties not required to be recorded under ASC 606.

[9] Change relates to noncurrent portion of deferred revenue in connection with the extended warranties not required to be recorded under ASC 606.

[10] Change relates to $177,000 cumulative effect adjustment on the adoption of ASC 606 and the net gain adjustment of $315,000 for the six months ended June 30, 2018.