Note 2 - Revenue Recognition (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Retained Earnings (Accumulated Deficit), Ending Balance	$ 441,877	$ 422,235
Contract with Customer Liability, Customer Deposits	5,400
Contract with Customer, Liability, Total	6,500	$ 5,600
Contract with Customer, Liability, Revenue Recognized	$ 1,400
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	3 years