Note 7 - Segment and Geographic Information - Customers with Sales and Accounts Receivable Greater Than 10% (Details) - Customer Concentration Risk [Member]		3 Months Ended			6 Months Ended				12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017		Dec. 31, 2017
Distributor A [Member] | Sales Revenue, Net [Member]
Concentration risk		20.00%	17.00%		20.00%		17.00%
Distributor A [Member] | Accounts Receivable [Member]
Concentration risk					19.00%				16.00%
Distributor B [Member] | Sales Revenue, Net [Member]
Concentration risk		10.00%		[1]	10.00%			[1]
Distributor B [Member] | Accounts Receivable [Member]
Concentration risk					15.00%					[1]
Distributor C [Member] | Sales Revenue, Net [Member]
Concentration risk	[1]
Distributor C [Member] | Accounts Receivable [Member]
Concentration risk						[1]			15.00%

[1] Represents less than 10%.