Note 8 - Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	20.40%	35.90%	24.30%	33.90%		35.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount				$ 13.6
Unrecognized Tax Benefits, Ending Balance	$ 43.2		$ 43.2
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	34.1		34.1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 4.1		$ 4.1
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%