Note 10 - Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				35.00%		35.00%
Effective Income Tax Rate Reconciliation, Percent, Total	26.70%	40.40%	26.00%	40.50%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent			4.70%	4.30%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent, Total			1.00%	1.30%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent			0.70%	0.10%
Income Taxes Paid, Net, Total			$ 12.0	$ 0.9
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%