Note 4 - Property and Equipment (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Depreciation, Depletion and Amortization, Total	$ 19.0	$ 15.8	$ 17.1
Capital Expenditure	54.3	80.5
Interest Paid, Capitalized, Investing Activities	3.8	2.6
Maritime Equipment [Member]
Property, Plant and Equipment, Additions	$ 40.2	42.8
Class Vessel [Member]
Property, Plant and Equipment, Additions		$ 27.2