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Note 2 - Summary of Significant Accounting Policies - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($)
Jun. 30, 2020
Dec. 31, 2019
Jun. 30, 2019
Dec. 31, 2018
Cash and cash equivalents $ 53,065,833 $ 65,249,072 $ 100,263,915 $ 100,652,809
Restricted cash-short term 0 95,737,862 11,248,400 11,452,078
Cash, cash equivalents and restricted cash $ 53,065,833 $ 160,986,934 175,992,939 180,396,910
Restricted cash-long term     $ 64,480,624 $ 68,292,023