Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Payments to Acquire Businesses, Gross		$ 8,000
Cash and Cash Equivalents, at Carrying Value, Ending Balance		109,587	83,431	$ 137,686	$ 90,642
Cash and Cash Equivalents, Period Increase (Decrease), Total		(28,100)
Accounts Receivable, after Allowance for Credit Loss, Current, Total		4,935		3,803
Restricted Cash and Cash Equivalents, Noncurrent, Total		1,540	1,524	1,534	$ 1,522
Foreign Currency Transaction Gain (Loss), Realized		0	$ 0
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance		$ 2,813		$ 2,698
Number of Operating Segments		1
AZEDRA [Member]
Payments to Acquire Businesses, Gross	$ 8,000