Note 2 - Revenue (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Retained Earnings (Accumulated Deficit), Ending Balance	$ 422,235	$ 366,164
Contract with Customer, Liability, Total	5,600	$ 6,400
Contract with Customer, Liability, Revenue Recognized	5,300
Accounting Standards Update 2014-09 [Member]
Retained Earnings (Accumulated Deficit), Ending Balance	$ 1,100
Minimum [Member]
Contracts With Customers, Term	1 year
Maximum [Member]
Contracts With Customers, Term	5 years