Note 1 - Nature of Operations and Summary of Significant Accounting Policies (Details Textual) $ in Millions		3 Months Ended	12 Months Ended
	Apr. 22, 2022	Dec. 31, 2022 USD ($) shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021	Jan. 01, 2020 USD ($)
Highly Liquid Investments Maturity Period (Year)			3 years
Inspection Interval (Year)			5 years
Increase Of Amortization Period (Month)			30 months
Number Of Offshore Supply Vessels			191	153
Number Of Vessels Disposed			8	18
Alucat Crew Boats, Expected Cost, Each			$ 3.5
Down Payment To Start Construction On Crew Boats			$ 1.2
Number of Ocean Going Tugs, Contracted To Build		2	2
Ocean Going Tugs, Expected Cost, Each		$ 6.3
Down Payments To Start Construction On Tugboats		$ 2.3
OCI, Debt Securities, Available-for-Sale, Transfer from Held-to-Maturity, Gain (Loss), before Adjustment and Tax			$ (0.5)
Government Assistance, Amount			1.3
Wage and Sick Cost Refund, Amount			$ 5.3
Accounting Standards Update 2016-13 [Member]
Accounts Receivable, Allowance for Credit Loss, Ending Balance					$ 0.2
Debt Security, Corporate, Non-US [Member]
Debt Instrument, Interest Rate, Stated Percentage		8.75%	8.75%
PEMEX [Member]
Accounts Receivable, before Allowance for Credit Loss, Current		$ 8.6	$ 8.6
Out-of-the-money Warrants [Member]
Class of Warrant or Right, Outstanding (in shares) | shares		5,923,399	5,923,399
Marine Equipment [Member]
Property, Plant and Equipment, Salvage Value, Percentage		7.50%	7.50%
Marine Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)			10 years
Marine Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)			20 years
Property, Plant and Equipment, Other Types [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)			3 years
Property, Plant and Equipment, Other Types [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)			10 years
Remaining Number Of Vessels [Member]
Number of Vessels			183	135
Actively Employed Vessels [Member]
Number of Vessels			178	126
Stacked Vessels [Member]
Number of Vessels			5	9
Alucat Crew Boats [Member]
Number of Vessels			2
Swire Pacific Offshore Holdings Ltd. [Member]
Number of Vessels, Offshore Support	50		50
Swire Pacific Offshore Holdings Ltd. [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)			1 year
Swire Pacific Offshore Holdings Ltd. [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)			16 years