Note 4 - Property and Equipment (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Depreciation, Total	$ 24,200	$ 19,000	$ 15,800
Payments to Acquire Property, Plant, and Equipment, Total	96,002	54,345	$ 80,485
Interest Paid, Capitalized, Investing Activities	3,700	3,800
Maritime Equipment [Member]
Property, Plant and Equipment, Additions	$ 72,700	$ 40,200