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Note 10 - Stockholders' Equity (Details Textual) |  |  |  |  | 12 Months Ended | 143 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 | Dec. 31, 2023 USD ($) $ / shares shares | Dec. 31, 2022 USD ($) $ / shares shares | Dec. 31, 2023 USD ($) $ / shares shares | Dec. 01, 2023 USD ($) | Sep. 15, 2022 USD ($) | 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 |  |  |  |  |
Shares Issued, Price Per Share (in dollars per share) | $ / shares |  |  |  |  | $ 19 |  |  |  |  |  |  |  |
Maximum Individual Common Stock Ownership, Percentage |  |  |  |  |  | 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] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Real Estate Properties |  |  |  |  |  | 12 |  | 12 |  |  |  |  |
Commercial Property [Member] | Partially Owned Properties [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Real Estate Properties |  |  |  |  |  | 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, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 0.17 |  |
Class of Warrant or Right, Exercised During Period (in shares) |  |  |  |  |  | 0 |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares) |  |  |  |  |  |  |  |  |  |  | 0.1 |  |
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 |  |
Class of Warrant or Right, Outstanding (in shares) |  |  |  |  |  |  |  |  |  |  | 14,450,069 |  |
Series D Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Authorized (in shares) |  |  |  |  |  | 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 |  |  |  |  |
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 |  |  |  |  |
Preferred Stock, Percentage of Outstanding Shares Required to Authorize Senior Ranking Stock |  |  |  |  |  | 66.67% |  | 66.67% |  |  |  |  |
Preferred Stock, Redemption Price Per Share (in dollars per share) | $ / shares |  |  |  |  |  | $ 25 |  | $ 25 |  |  |  |  |
Preferred Stock, Dividends Per Share, Declared (in dollars per share) | $ / shares |  |  |  |  |  | $ 2.34372 | $ 2.34372 |  |  |  |  |  |
Payments of Dividends | $ |  |  |  |  |  | $ 2,100,000 | $ 2,200,000 |  |  |  |  |  |
Stock Repurchase Program, Authorized Amount | $ |  |  |  |  |  |  |  |  | $ 4,000,000 | $ 4,000,000 |  |  |
Stock Repurchased During Period, Shares (in shares) |  |  |  |  |  | 23,041 | 6,013 |  |  |  |  |  |
Stock Repurchased, Average Cost Per Share (in dollars per share) | $ / shares |  |  |  |  |  | $ 15.97 | $ 20.31 |  |  |  |  |  |
Stock Repurchased, Commission Per Share (in dollars per share) | $ / shares |  |  |  |  |  | $ 0.035 | $ 0.035 |  |  |  |  |  |
Stock Repurchased During Period, Value | $ |  |  |  |  |  | $ 200,000 | $ 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 | $ |  |  |  |  |  | $ 1,200,000 | $ 3,100,000 |  |  |  |  |  |
Common Stock, Shares Authorized (in shares) |  |  |  |  |  | 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 |  |  |  |  |
Common Stock, Shares, Issued (in shares) |  |  |  |  |  | 11,859,726 | 11,807,893 | 11,859,726 |  |  |  |  |
Stock Repurchase Program, Authorized Amount | $ |  |  |  |  |  |  |  |  | $ 6,000,000 | $ 6,000,000 |  | $ 10,000,000 |
Stock Repurchased During Period, Shares (in shares) |  |  |  |  |  |  | 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 |  |  |  |  |
Common Stock, Shares, Issued (in shares) |  |  |  |  |  | 0 |  | 0 |  |  |  |  |
Common Class C [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Shares Authorized (in shares) |  |  |  |  |  | 9,000,000 |  | 9,000,000 |  |  |  |  |
Common Stock, Shares, Issued (in shares) |  |  |  |  |  | 0 |  | 0 |  |  |  |  |
Common Stock, Number of Entitled Votes |  |  |  |  |  | 1 |  | 1 |  |  |  |  |

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