Note 7 - Debt (Details Textual) | Jun. 29, 2018USD ($) | Jun. 01, 2018USD ($) | Feb. 08, 2018USD ($) | Jan. 05, 2018USD ($) | Dec. 14, 2017USD ($) | Sep. 05, 2017 | Mar. 31, 2019USD ($) | Jun. 30, 2018USD ($)$ / shares | Dec. 31, 2018 | May 31, 2018 | Jun. 30, 2018USD ($)$ / shares |
Line of Credit Facility, Remaining Borrowing Capacity | | | | | | | | $ 61,929,000 | | | $ 61,929,000 |
M/T Eco Marina Del Ray [Member] | | | | | | | | | | | |
Sale Leaseback Transaction, Lease Term | 5 years | | | | | | | | | | |
Sale Leaseback Transaction, Rent Expense, Per Day | $ 8.60 | | | | | | | | | | |
Sale Leaseback Transaction, Buy Back, Amount | $ 22,680 | | | | | | | | | | |
Scenario, Forecast [Member] | M/T Eco Marina Del Ray [Member] | | | | | | | | | | | |
Sale Leaseback Transaction, Gross Proceeds, Investing Activities | | | | | | | $ 32,400 | | | | |
Unsecured Notes [Member] | | | | | | | | | | | |
Proceeds from Short-term Debt, Total | | | $ 6,400,000 | $ 5,369,000 | $ 12,500,000 | | | | | | |
Debt Instrument, Additional Revolving Options | | | | $ 4,631,000 | | | | | | | |
Notes Payable, Total | | | | | | | | 5,836,000 | | | 5,836,000 |
Unsecured Notes [Member] | Second Crede Note, First Revolving Option [Member] | | | | | | | | | | | |
Debt Instrument, Additional Revolving Options | | | | | $ 5,000,000 | | | | | | |
Unsecured Notes [Member] | Interest on Debt for the First Ninety Days [Member] | | | | | | | | | | | |
Debt Instrument, Interest Rate, Stated Percentage | | | | | 2.00% | | | | | | |
Unsecured Notes [Member] | Interest on Debt for Ninety up to 180 Days [Member] | | | | | | | | | | | |
Debt Instrument, Interest Rate, Stated Percentage | | | | | 10.00% | | | | | | |
Unsecured Notes [Member] | Interest on Debt 180 Days and Thereafter [Member] | | | | | | | | | | | |
Debt Instrument, Interest Rate, Stated Percentage | | | | | 15.00% | | | | | | |
Unsecured Notes [Member] | Second Crede Note, Second Revolving Option [Member] | | | | | | | | | | | |
Debt Instrument, Additional Revolving Options | | | | | $ 5,000,000 | | | | | | |
The ABN Bank [Member] | | | | | | | | | | | |
Long-term Line of Credit, Total | | | | | | | | $ 50,350,000 | | | $ 50,350,000 |
The ABN Bank [Member] | M/T Eco Fleet and M/T Eco Revolution [Member] | London Interbank Offered Rate (LIBOR) [Member] | | | | | | | | | | | |
Debt Instrument, LIBOR Rate | | | | | | | | 2.36% | | | 2.36% |
Norddeutsche Landesbank Girozentrale Bank [Member] | | | | | | | | | | | |
Long-term Line of Credit, Total | | | | | | | | $ 19,093,000 | | | $ 19,093,000 |
Norddeutsche Landesbank Girozentrale Bank [Member] | M/T Stenaweco Excellence [Member] | London Interbank Offered Rate (LIBOR) [Member] | | | | | | | | | | | |
Debt Instrument, LIBOR Rate | | | | | | | | 2.32% | | | 2.32% |
Alpha Bank [Member] | | | | | | | | | | | |
Long-term Line of Credit, Total | | | | | | | | $ 21,350,000 | | | $ 21,350,000 |
Alpha Bank [Member] | M/T Stenaweco Excellence [Member] | London Interbank Offered Rate (LIBOR) [Member] | | | | | | | | | | | |
Debt Instrument, LIBOR Rate | | | | | | | | 2.33% | | | 2.33% |
AT Bank [Member] | Predelivery Facility to Fund Hull No 2648 [Member] | | | | | | | | | | | |
Long-term Line of Credit, Total | | | | | | | | $ 0 | | | $ 0 |
Line of Credit Facility, Commitment Fee Percentage | | 0.00% | | | | | | | | 4.25% | |
Proceeds from Lines of Credit, Total | | | | | | | | | | | $ 7,494,000 |
Debt Instrument, Applicable Three Month LIBOR, Rate | | | | | | | | 2.32% | | | 2.32% |
Line of Credit Facility, Maximum Borrowing Capacity | | | | | | | | $ 8,993,000 | | | $ 8,993,000 |
AT Bank [Member] | AT Bank Second Predelivery Facility [Member] | | | | | | | | | | | |
Long-term Line of Credit, Total | | | | | | | | 1,690,000 | | | 1,690,000 |
Line of Credit Facility, Commitment Fee Percentage | | 0.00% | | | | | | | | | |
Line of Credit Facility, Remaining Borrowing Capacity | | | | | | | | 8,450,000 | | | $ 8,450,000 |
Proceeds from Lines of Credit, Total | | | | | | | | $ 1,690,000 | | | |
Debt Instrument, Applicable Three Month LIBOR, Rate | | | | | | | | 2.30% | | | 2.30% |
Line of Credit Facility, Maximum Borrowing Capacity | | $ 10,140,000 | | | | | | | | | |
Debt Instrument, Number of Available Tranches | | 5 | | | | | | | | | |
Debt Instrument, Number of Capital Expenditure Payments to be Made with Proceeds | | 5 | | | | | | | | | |
Debt Covenant, Ratio of Total Net Debt to Fleet Value | | 75.00% | | | | | | | | | |
Minimum Free Liquidity, Per Collateralized Vessel | | $ 750,000 | | | | | | | | | |
Minimum Free Liquidity, Per Bareboated Chartered-in Vessel | | $ 500,000 | | | | | | | | | |
AT Bank [Member] | London Interbank Offered Rate (LIBOR) [Member] | Predelivery Facility to Fund Hull No 2648 [Member] | | | | | | | | | | | |
Debt Instrument, Basis Spread on Variable Rate | | 6.30% | | | | | | | | 8.50% | |
AT Bank [Member] | London Interbank Offered Rate (LIBOR) [Member] | AT Bank Second Predelivery Facility [Member] | | | | | | | | | | | |
Debt Instrument, Basis Spread on Variable Rate | | 6.30% | | | | | | | | | |
AT Bank [Member] | London Interbank Offered Rate (LIBOR) [Member] | AT Bank Second Predelivery Facility [Member] | Scenario, Forecast [Member] | | | | | | | | | | | |
Debt Instrument, Basis Spread on Variable Rate | | | | | | | | | 6.00% | | |
AT Bank [Member] | M/T Eco Palm Desert [Member] | | | | | | | | | | | |
Line of Credit Facility, Commitment Fee Percentage | | 1.30% | | | | 2.00% | | | | | |
Line of Credit Facility, Remaining Borrowing Capacity | | | | | | | | $ 23,500,000 | | | $ 23,500,000 |
Family Trading [Member] | Immediate Family Member of Management or Principal Owner [Member] | Revolving Credit Facility [Member] | | | | | | | | | | | |
Long-term Line of Credit, Total | | | | | | | | 5,280,000 | | | 5,280,000 |
Line of Credit Facility, Remaining Borrowing Capacity | | | | | | | | 6,572,000 | | | 6,572,000 |
Proceeds from Lines of Credit, Total | | | | | | | | | | | 5,280,000 |
Debt Issuance Costs, Net, Total | | | | | | | | 170,000 | | | 170,000 |
Debt Instrument, Unamortized Discount, Total | | | | | | | | $ 4,330,000 | | | 4,330,000 |
Amortization of Debt Discount (Premium) | | | | | | | | | | | 140,000 |
Debt Related Commitment Fees and Debt Issuance Costs | | | | | | | | | | | 142,000 |
Interest Expense, Related Party | | | | | | | | | | | $ 27,000 |
Debt Instrument, Convertible, Conversion Price | $ / shares | | | | | | | | $ 0.60 | | | $ 0.60 |
Debt Instrument, Convertible, Number of Equity Instruments | | | | | | | | | | | 8,800,000 |