Note 3 - Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Jun. 30, 2018	Dec. 31, 2017
Deferred Tax Liabilities, Net, Total		$ 111.3
Deferred Tax Assets, Valuation Allowance, Total		79.4	$ 78.7
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member]
Deferred Tax Liabilities, Net, Total		0.3
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ (15.0)
Canada Revenue Agency [Member] | Foreign Tax Authority [Member]
Deferred Tax Liabilities, Net, Total		112.5
Mexican Tax Authority [Member] | Foreign Tax Authority [Member]
Deferred Tax Liabilities, Net, Total		$ 1.5