Note 5 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Income Taxes	$ 800
Income Tax Expense (Benefit), Total	$ (381)	$ (1,162)
Effective Income Tax Rate Reconciliation, Percent, Total	47.00%	180.00%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				35.00%
Unrecognized Tax Benefits, Ending Balance	$ 13,400			$ 12,900
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	7,900			7,700
Unrecognized Tax Benefits In Long Term Liabilities	3,000
Unrecognized Tax Benefits In Deferred Tax Assets	10,400
Unrecognized Tax Benefits In Deferred Tax Asset Subject To Full Valuation Allowance	5,500
Deferred Tax Assets, Valuation Allowance, Total	$ 9,000			$ 9,100
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%