Note 8 - Income Taxes (Details Textual) - USD ($)		3 Months Ended		12 Months Ended
	Dec. 22, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		$ 2,600,000			$ 2,600,000
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0
Unrecognized Tax Benefits, Interest on Income Taxes Accrued		166,000			166,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability					$ (82,900,000)
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount		$ 22,000	$ (1,100,000)
Domestic Tax Authority [Member] | Earliest Tax Year [Member]
Open Tax Year		2014
Domestic Tax Authority [Member] | Latest Tax Year [Member]
Open Tax Year		2017
State and Local Jurisdiction [Member] | Earliest Tax Year [Member]
Open Tax Year		2013
State and Local Jurisdiction [Member] | Latest Tax Year [Member]
Open Tax Year		2017
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				21.00%