Note 13 - Income Taxes (Details Textual) - USD ($) $ in Thousands	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, Percent, Total	20.80%	31.80%	19.80%	34.10%
Income Tax Expense (Benefit), Total	$ 14,028	$ 28,517	$ 38,513	$ 60,651
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent						35.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Amount, Total	3,200		11,300
Deferred Tax Assets, Net, Total	$ 36,800		$ 36,800			$ 41,500
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%