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Note 2 - Revenue Recognition (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Retained Earnings (Accumulated Deficit), Ending Balance	$ (25,256)		$ (25,256)			$ (27,089)
Capitalized Contract Cost, Net, Total					$ 500
Contract with Customer, Liability, Noncurrent	500		500		900
Contract with Customer, Liability, Revenue Recognized	5,000		7,600
Revenue, Remaining Performance Obligation, Amount	45,300		45,300
Contract with Customer, Performance Obligation Satisfied in Previous Period	200		300
Capitalized Contract Cost, Amortization	100		200
Capitalized Contract Cost, Impairment Loss	0		0
Prepaid Expenses and Other Current Assets [Member]
Contract with Customer, Asset, Net, Current, Total	3,200		3,200		1,900
Prepaid Expenses and Other Current Assets and Other Non-current Assets [Member]
Deferred Costs, Total	$ 400		$ 400			$ 600
Customer Concentration Risk [Member] \| Sales Revenue, Net [Member] \| Transferred over Time [Member]
Concentration Risk, Percentage	68.00%		32.00%
Geographic Concentration Risk [Member] \| Sales Revenue, Net [Member]
Concentration Risk, Percentage	100.00%	100.00%	100.00%	100.00%
Geographic Concentration Risk [Member] \| Sales Revenue, Net [Member] \| Countries other than the United States [Member]
Concentration Risk, Percentage	57.00%	62.00%	58.00%	57.00%
Accounting Standards Update 2014-09 [Member]
Retained Earnings (Accumulated Deficit), Ending Balance					(4,400)
Accounts Receivable, Net, Total					800
Contract with Customer, Asset, Net, Total					1,900
Contract with Customer, Liability, Total					$ (2,500)