Related Party Transactions - Transfers of Participation Interest (Details)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Related Party Transaction
Loans and Leases Receivable, Gross	$ 177,232,669	$ 202,951,903
Percentage Ownership Sold	0.6911
Debt Instrument, Face Amount	$ 176,784,964	201,624,466
14th & Alice Street Owner, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	19,728,938	12,957,731
Debt Instrument, Face Amount	19,610,084	12,932,034
2539 Morse, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		7,067,422
Debt Instrument, Face Amount		7,000,000
370 Lex Part Deux, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	49,734,503	48,425,659
Debt Instrument, Face Amount	49,668,256	48,349,948
Austin H. I. Owner LLC
Related Party Transaction
Loans and Leases Receivable, Gross		3,531,776
Debt Instrument, Face Amount		3,500,000
City Gardens 333 LLC (2)
Related Party Transaction
Loans and Leases Receivable, Gross	28,917,582	28,056,179
Debt Instrument, Face Amount	28,905,569	28,049,717
High Pointe Mezzanine Investments, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		3,263,285
Debt Instrument, Face Amount		3,000,000
NB Private Capital, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	20,172,593	20,166,610
Debt Instrument, Face Amount	20,000,000	20,000,000
Orange Grove Property Investors, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	10,697,792	10,696,587
Debt Instrument, Face Amount	10,600,000	10,600,000
RS JZ Driggs, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	8,283,124	8,286,629
Debt Instrument, Face Amount	8,200,000	8,200,000
SparQ Mezz Borrower, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		8,783,139
Debt Instrument, Face Amount		8,700,000
Stonewall Station Mezz LLC
Related Party Transaction
Loans and Leases Receivable, Gross	9,936,287	9,875,162
Debt Instrument, Face Amount	9,851,847	9,792,767
The Bristol at Southport, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		23,661,724
Debt Instrument, Face Amount		23,500,000
TSG-Parcel 1, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	18,180,000	18,180,000
Debt Instrument, Face Amount	18,000,000	18,000,000
Windy Hill PV Five CM, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	11,581,850
Debt Instrument, Face Amount	11,949,208
Obligations Under Participation Agreements
Related Party Transaction
Loans and Leases Receivable, Gross	67,670,405	103,186,327
Debt Instrument, Face Amount	67,624,467	102,564,795
Obligations Under Participation Agreements | 14th & Alice Street Owner, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	$ 15,752,112	$ 10,387,090
Percentage Ownership Sold	0.8000	0.8000
Debt Instrument, Face Amount	$ 15,688,067	$ 10,345,627
Obligations Under Participation Agreements | 2539 Morse, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		$ 2,825,519
Percentage Ownership Sold		0.4000
Debt Instrument, Face Amount		$ 2,800,001
Obligations Under Participation Agreements | 370 Lex Part Deux, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	$ 17,383,890	$ 22,724,476
Percentage Ownership Sold	0.3500	0.4700
Debt Instrument, Face Amount	$ 17,383,890	$ 22,724,476
Obligations Under Participation Agreements | Austin H. I. Owner LLC
Related Party Transaction
Loans and Leases Receivable, Gross		$ 1,059,532
Percentage Ownership Sold		0.3000
Debt Instrument, Face Amount		$ 1,050,000
Obligations Under Participation Agreements | City Gardens 333 LLC (2)
Related Party Transaction
Loans and Leases Receivable, Gross	$ 4,048,428	$ 13,184,648
Percentage Ownership Sold	0.1400	0.4700
Debt Instrument, Face Amount	$ 4,046,781	$ 13,182,584
Obligations Under Participation Agreements | High Pointe Mezzanine Investments, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		$ 1,217,160
Percentage Ownership Sold		0.3720
Debt Instrument, Face Amount		$ 1,116,000
Obligations Under Participation Agreements | NB Private Capital, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	$ 3,362,098	$ 14,601,021
Percentage Ownership Sold	0.1667	0.7240
Debt Instrument, Face Amount	$ 3,333,333	$ 14,480,392
Obligations Under Participation Agreements | Orange Grove Property Investors, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	$ 8,558,182	$ 8,557,205
Percentage Ownership Sold	0.8000	0.8000
Debt Instrument, Face Amount	$ 8,480,000	$ 8,480,000
Obligations Under Participation Agreements | RS JZ Driggs, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	$ 4,140,330	$ 4,142,264
Percentage Ownership Sold	0.5000	0.5000
Debt Instrument, Face Amount	$ 4,100,000	$ 4,100,000
Obligations Under Participation Agreements | SparQ Mezz Borrower, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		$ 3,231,689
Percentage Ownership Sold		0.3681
Debt Instrument, Face Amount		$ 3,202,454
Obligations Under Participation Agreements | Stonewall Station Mezz LLC
Related Party Transaction
Loans and Leases Receivable, Gross	$ 4,371,496	$ 4,344,635
Percentage Ownership Sold	0.4400	0.4400
Debt Instrument, Face Amount	$ 4,334,813	$ 4,308,817
Obligations Under Participation Agreements | The Bristol at Southport, LLC
Related Party Transaction
Loans and Leases Receivable, Gross		$ 10,043,088
Percentage Ownership Sold		0.4244
Debt Instrument, Face Amount		$ 9,974,444
Obligations Under Participation Agreements | TSG-Parcel 1, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	$ 2,020,000	$ 6,868,000
Percentage Ownership Sold	0.1111	0.3778
Debt Instrument, Face Amount	$ 2,000,000	$ 6,800,000
Obligations Under Participation Agreements | Windy Hill PV Five CM, LLC
Related Party Transaction
Loans and Leases Receivable, Gross	8,033,869
Debt Instrument, Face Amount	$ 8,257,583