Fair value measurement - Not carried at Fair Value (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal Balance	$ 402,687,438	$ 377,388,317
Loans and Leases Receivable, Gross		378,612,768
Loans Receivable, Fair Value Disclosure	399,609,378	379,160,415
Loans and Leases Receivable, Allowance	(1,144,994)	0
Other Liabilities, Fair Value Disclosure		229,270,597
Debt Instrument, Face Amount	176,784,964	201,624,466
Secured Debt	177,232,669	202,951,903
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and Leases Receivable, Gross	402,969,513
Loans Receivable, Fair Value Disclosure	399,609,378
Other Liabilities, Fair Value Disclosure	231,885,180
Debt Instrument, Face Amount	239,652,851	228,313,711
Secured Debt	238,640,684	227,548,397
Long-term Debt, Fair Value		229,270,597
Loans Held for Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal Balance		374,267,430
Loans and Leases Receivable, Gross		375,462,222
Loans Receivable, Fair Value Disclosure		375,956,154
Loans Held for Investment \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal Balance	398,694,704
Loans and Leases Receivable, Gross	400,076,940
Loans Held For Investment Acquired Through Participation
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal Balance	3,992,734	3,120,887
Loans and Leases Receivable, Gross		3,150,546
Loans Receivable, Fair Value Disclosure		3,204,261
Loans Held For Investment Acquired Through Participation \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and Leases Receivable, Gross	4,037,567
Discounted Cash Flow \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		379,160,415
Discounted Cash Flow \| Mortgage Agreement Payable [Member] \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities, Fair Value Disclosure	44,813,764
Debt Instrument, Face Amount	44,481,855	44,614,480
Secured Debt	44,687,123	44,753,633
Long-term Debt, Fair Value		44,947,378
Discounted Cash Flow \| Loans Held for Investment \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure	395,581,145	375,956,154
Other Liabilities, Fair Value Disclosure		81,134,436
Discounted Cash Flow \| Loans Held For Investment Acquired Through Participation \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure	4,028,233	3,204,261
Discounted Cash Flow \| Obligations Under Participation Agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities, Fair Value Disclosure		103,188,783
Discounted Cash Flow \| Obligations Under Participation Agreements \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities, Fair Value Disclosure	59,524,887
Debt Instrument, Face Amount	67,624,467	102,564,795
Secured Debt	67,670,405	103,186,327
Long-term Debt, Fair Value		103,188,783
Discounted Cash Flow \| Repurchase Agreement Payable \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities, Fair Value Disclosure	92,546,529
Debt Instrument, Face Amount	92,546,529	81,134,436
Secured Debt	91,352,312	79,608,437
Long-term Debt, Fair Value		81,134,436
Discounted Cash Flow \| Revolving Credit Facility Payable [Member] \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities, Fair Value Disclosure	35,000,000
Debt Instrument, Face Amount	35,000,000	0
Secured Debt	$ 34,930,844	0
Long-term Debt, Fair Value		$ 0

Face (par) amount of debt instrument at time of issuance.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Fair value portion of other liabilities.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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