Note 10 - Income Taxes (Details Textual)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				35.00%
Effective Income Tax Rate Reconciliation, Percent, Total	24.30%	41.10%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	4.70%	4.40%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent, Total	0.80%	1.90%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent	2.20%	0.20%
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%