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Note 11 - Long-term Debt (Details Textual) |  |  |  |  |  |  |  |  |  | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 17, 2018 USD ($) | Feb. 08, 2018 USD ($) | Jan. 10, 2018 USD ($) | Jan. 10, 2018 USD ($) | Dec. 11, 2017 USD ($) | May 16, 2017 USD ($) | Sep. 15, 2016 USD ($) | Jun. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Dec. 20, 2013 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Feb. 14, 2018 USD ($) | Dec. 07, 2017 USD ($) | Mar. 01, 2017 USD ($) | May 18, 2016 USD ($)
Proceeds from Issuance of Debt |  |  |  |  |  |  |  |  |  |  | $ 43,000,000 |  |  |  |  |  |
Long-term Debt, Total |  |  |  |  |  |  |  |  |  |  | 386,975,841 | $ 400,229,914 |  |  |  |  |
Term Loan Financial Covenants, Cash Requirement |  |  |  |  |  |  |  |  |  |  | 7,917,738 |  |  |  |  |  |
Debt Issuance Costs, Gross |  |  |  |  |  |  |  |  |  |  | 7,871,170 | 7,055,914 |  |  |  |  |
Amortization of Debt Issuance Costs |  |  |  |  |  |  |  |  |  |  | $ 690,841 | $ 715,587 | $ 587,157 |  |  |  |
Debt, Weighted Average Interest Rate |  |  |  |  |  |  |  |  |  |  | 3.97% | 3.43% | 2.67% |  |  |  |
Interest Expense, Debt, Total |  |  |  |  |  |  |  |  |  |  | $ 15,640,377 | $ 14,149,326 | $ 10,175,944 |  |  |  |
Interest Costs Capitalized |  |  |  |  |  |  |  |  |  |  | 813,423 | $ 1,660,802 | $ 1,822,443 |  |  |  |
Long-term Line of Credit, Total |  |  |  |  |  |  |  |  |  |  | $ 125,260,000 |  |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value to Term Loan Ratio |  |  |  |  |  |  |  |  |  |  | 130.00% |  |  |  |  |  |
Percentage of Total Debt to Total Market Value Adjusted Assets |  |  |  |  |  |  |  |  |  |  | 80.00% |  |  |  |  |  |
Percentage of Dividends Paid to Free Cash Flow |  |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |
Quarterly Commitment Fee Percentage |  |  |  |  |  |  |  |  |  |  | 0.77% |  |  |  |  |  |
Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Basis Spread on Variable Rate |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |  |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value to Term Loan Ratio |  |  |  |  |  |  |  |  |  |  | 125.00% |  |  |  |  |  |
EBITDA to Interest Expense Ratio |  |  |  |  |  |  |  |  |  |  | 2.5 |  |  |  |  |  |
Quarterly Commitment Fee Percentage |  |  |  |  |  |  |  |  |  |  | 0.70% |  |  |  |  |  |
Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Basis Spread on Variable Rate |  |  |  |  |  |  |  |  |  |  | 0.80% |  |  |  |  |  |
Condition Met At Delivery [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  |  |  |  |  |  | $ 67,200,000 |  |  |  |  |  |  |
Percentage of Fair Market Value of Vessel Subject to the Minimum Employment Condition |  |  |  |  |  |  |  |  |  | 70.00% |  |  |  |  |  |  |
Condition Not Being Met [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  |  |  |  |  |  | $ 62,400,000 |  |  |  |  |  |  |
Percentage of Fair Market Value of Vessel Subject to the Minimum Employment Condition |  |  |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |
Term Loan Entered Into on December 20, 2013 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  |  |  |  | $ 15,600,000 | $ 16,000,000 |  |  |  |  |  |  |  |
Term Loan Entered Into on May 18, 2016 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  |  | $ 32,500,000 |  |  |  |  |  |  |  |  |  |  |
Term Loan Entered Into on May 18, 2016 [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  | $ 33,150,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term Loan Entered Into on May 18, 2016 [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Maximum Borrowing Capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 74,480,000
Term Loan Entered into on January 30, 2009 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  |  |  | $ 24,600,000 |  |  |  |  |  |  |  |  |  |
Term Loan Entered Into March 1, 2017 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Maximum Borrowing Capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 76,020,000 |
Term Loan Entered Into March 1, 2017 [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt | $ 35,262,500 |  |  | $ 35,525,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Term Loan Entered December 7, 2017 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  | $ 10,500,000 |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Maximum Borrowing Capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 22,500,000 |  |
Term Loan Entered December 7, 2017 [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  | $ 11,775,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term Loan Refinanced on a Long Term Basis [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term Debt, Total |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 27,675,000 |  |  |

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- Definition Percentage of Free Cash Flow allowed to be paid as dividends under current loan covenants. + References No definition available. + Details
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- Definition Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399 + Details
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