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Note 10 - Stockholders' Equity (Details Textual) |  |  |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended | 140 Months Ended |  |  |  |
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Jul. 12, 2021 $ / shares shares | Jun. 17, 2021 USD ($) shares | Jun. 17, 2021 USD ($) shares | Jun. 15, 2021 USD ($) $ / shares shares | Jan. 23, 2012 USD ($) $ / shares shares | Sep. 30, 2023 USD ($) $ / shares shares | Sep. 30, 2022 USD ($) | Sep. 30, 2023 USD ($) $ / shares shares | Sep. 30, 2022 USD ($) $ / shares | Dec. 31, 2022 USD ($) $ / shares shares | Sep. 30, 2023 USD ($) $ / shares shares | Sep. 15, 2022 USD ($) | Jan. 21, 2022 $ / shares shares | Sep. 17, 2021 USD ($) | Aug. 31, 2021 $ / shares shares
Preferred Stock, Shares Authorized (in shares) |  |  |  |  |  | 1,000,000 |  | 1,000,000 |  |  | 1,000,000 |  |  |  |
Shares Issued, Price Per Share (in dollars per share) | $ / shares |  |  |  |  | $ 19 |  |  |  |  |  |  |  |  |  |
Maximum Individual Common Stock Ownership, Percentage |  |  |  |  |  | 9.80% |  | 9.80% |  |  | 9.80% |  |  |  |
Number of Limited Partnerships in which Company is Sole General Partner |  |  |  |  |  |  |  | 5 |  |  |  |  |  |  |
Registered Shares of Common Stock Pursuant to Dividend Reinvestment Plan (in shares) |  |  |  |  | 3,000,000 |  |  |  |  |  |  |  |  |  |
Common Stock, Percentage of Purchase Price Per Share |  |  |  |  | 95.00% |  |  |  |  |  |  |  |  |  |
Payment of Sales, Commission or Dealer Manager Fee | $ |  |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |
Notice Period for Amendments to Dividend Reinvestment Plan (Day) |  |  |  |  | 30 days |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Value, Dividend Reinvestment Plan | $ |  |  |  |  |  |  |  |  |  |  | $ 17,400,000 |  |  |  |
Stock Issued During Period, Shares, Dividend Reinvestment Plan (in shares) |  |  |  |  |  |  |  |  |  |  | 917,074 |  |  |  |
Commercial Property [Member] | Partially Owned Properties [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Real Estate Properties |  |  |  |  |  | 2 |  | 2 |  |  | 2 |  |  |  |
Class A Common Stock and Accompanying Common Stock Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares Issued, Price Per Share (in dollars per share) | $ / shares | $ 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class A Common Stock and Accompanying Pre-funded Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares Issued, Price Per Share (in dollars per share) | $ / shares | $ 4.99 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | $ 5.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrants and Rights Outstanding, Term (Year) | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-funded Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares | $ 0.01 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Placement Agent Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 80,000
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6.25
Warrants and Rights Outstanding, Term (Year) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years
Class of Warrant or Right, Securities Called By Warrants or Rights, Percentage of Class of Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.00%
Common Stock Warrants and Placement Agent Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercised During Period (in shares) |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |
Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 7 |  |
Warrants and Rights Outstanding, Term (Year) |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |
Series D Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Authorized (in shares) |  |  |  |  |  | 1,000,000 |  | 1,000,000 |  | 1,000,000 | 1,000,000 |  |  |  |
Stock Issued During Period, Shares, New Issues (in shares) |  | 920,000 |  | 800,000 |  |  |  |  |  |  |  |  |  |  |
Shares Issued, Price Per Share (in dollars per share) | $ / shares |  |  |  | $ 25 |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock | $ |  | $ 20,500,000 |  | $ 18,100,000 |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Dividend Rate, Percentage |  |  |  |  |  |  |  | 9.375% |  |  |  |  |  |  |
Preferred Stock, Liquidation Preference Per Share (in dollars per share) | $ / shares |  |  |  |  |  | $ 25 |  | $ 25 |  | $ 25 | $ 25 |  |  |  |
Preferred Stock, Dividend Rate, Per-Dollar-Amount (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 2.34375 |  |  |  |  |  |  |
Preferred Stock, Number of Board of Directors Entitled to Vote if Dividends not Paid for 18 Monthly Dividend Periods |  |  |  |  |  | 2 |  | 2 |  |  | 2 |  |  |  |
Preferred Stock, Percentage of Outstanding Shares Required to Authorize Senior Ranking Stock |  |  |  |  |  | 66.67% |  | 66.67% |  |  | 66.67% |  |  |  |
Preferred Stock, Redemption Price Per Share (in dollars per share) | $ / shares |  |  |  |  |  | $ 25 |  | $ 25 |  |  | $ 25 |  |  |  |
Preferred Stock, Dividends Per Share, Declared (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 1.75779 | $ 1.75779 |  |  |  |  |  |
Payments of Dividends | $ |  |  |  |  |  |  |  | $ 500,000 | $ 500,000 |  |  |  |  |  |
Stock Repurchase Program, Authorized Amount | $ |  |  |  |  |  |  |  |  |  |  |  | $ 4,000,000 |  |  |
Stock Repurchased During Period, Shares (in shares) |  |  |  |  |  |  |  | 15,047 |  | 6,013 |  |  |  |  |
Stock Repurchased, Average Cost Per Share (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 16.67 |  | $ 20.31 |  |  |  |  |
Stock Repurchased, Commission Per Share (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 0.035 |  | $ 0.035 |  |  |  |  |
Stock Repurchased During Period, Value | $ |  |  |  |  |  |  |  | $ 250,769 |  | $ 122,141 |  |  |  |  |
Series D Preferred Stock [Member] | Monthly Dividends [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Dividends Per Share, Declared (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 0.19531 |  |  |  |  |  |  |
Series D Preferred Stock [Member] | Over-Allotment Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues (in shares) |  |  | 120,000 |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock | $ |  |  | $ 2,700,000 |  |  |  |  |  |  |  |  |  |  |  |
Option to Purchase Additional Shares, Period (Day) |  |  |  | 45 days |  |  |  |  |  |  |  |  |  |  |
Common Class A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues (in shares) | 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments of Dividends | $ |  |  |  |  |  | $ 300,000 | $ 200,000 | $ 900,000 | $ 2,900,000 |  |  |  |  |  |
Common Stock, Shares Authorized (in shares) |  |  |  |  |  | 100,000,000 |  | 100,000,000 |  | 100,000,000 | 100,000,000 |  |  |  |
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares |  |  |  |  |  | $ 0.01 |  | $ 0.01 |  | $ 0.01 | $ 0.01 |  |  |  |
Common Stock, Shares, Issued (in shares) |  |  |  |  |  | 11,859,726 |  | 11,859,726 |  | 11,807,893 | 11,859,726 |  |  |  |
Stock Repurchase Program, Authorized Amount | $ |  |  |  |  |  |  |  |  |  |  |  | $ 6,000,000 |  | $ 10,000,000 |
Stock Repurchased During Period, Shares (in shares) |  |  |  |  |  |  |  | 0 |  | 196,631 |  |  |  |  |
Stock Repurchased, Average Cost Per Share (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  | $ 1.59 |  |  |  |  |
Stock Repurchased, Commission Per Share (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  | $ 0.035 |  |  |  |  |
Stock Repurchased During Period, Value | $ |  |  |  |  |  |  |  |  |  | $ 313,578 |  |  |  |  |
Common Class B [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Shares Authorized (in shares) |  |  |  |  |  | 1,000 |  | 1,000 |  |  | 1,000 |  |  |  |
Common Stock, Shares, Issued (in shares) |  |  |  |  |  | 0 |  | 0 |  |  | 0 |  |  |  |
Common Class C [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Shares Authorized (in shares) |  |  |  |  |  | 9,000,000 |  | 9,000,000 |  |  | 9,000,000 |  |  |  |
Common Stock, Shares, Issued (in shares) |  |  |  |  |  | 0 |  | 0 |  |  | 0 |  |  |  |
Common Stock, Number of Entitled Votes |  |  |  |  |  | 1 |  | 1 |  |  | 1 |  |  |  |

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- Definition Represents the securities called by warrants or rights, expressed as a percentage of the specified class of stock. + References No definition available. + Details
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- Definition Number of securities into which each warrant or right may be converted. For example, but not limited to, each warrant may be converted into two shares. + References No definition available. + Details
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- Definition Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481112/505-10-50-3 + Details
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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
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- Definition The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(d)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481112/505-10-50-3 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481112/505-10-50-4 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481112/505-10-50-13 + Details
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