FAIR VALUE OF FINANCIAL INSTRUMENTS (Summary of Significant Unobservable Inputs used to Value Investments) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2020 Y USD ($)	Dec. 31, 2019 USD ($) Y
Development Property Investments [Member] \| Minimum [Member] \| Income Approach Analysis [Member] \| Market Yields/Discount Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.0694	0.0689
Development Property Investments [Member] \| Minimum [Member] \| Income Approach Analysis [Member] \| Exit Date [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.83	1.50
Development Property Investments [Member] \| Minimum [Member] \| Option Pricing Model [Member] \| Volatility [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.6703	0.6095
Development Property Investments [Member] \| Minimum [Member] \| Option Pricing Model [Member] \| Market Yields/Discount Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.0825	0.0775
Development Property Investments [Member] \| Minimum [Member] \| Option Pricing Model [Member] \| Exit Date [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.83	1.50
Development Property Investments [Member] \| Minimum [Member] \| Option Pricing Model [Member] \| Capitalization Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.0525	0.0475
Development Property Investments [Member] \| Maximum [Member] \| Income Approach Analysis [Member] \| Market Yields/Discount Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.0916	0.1016
Development Property Investments [Member] \| Maximum [Member] \| Income Approach Analysis [Member] \| Exit Date [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	5.94	6.69
Development Property Investments [Member] \| Maximum [Member] \| Option Pricing Model [Member] \| Volatility [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.9675	0.9383
Development Property Investments [Member] \| Maximum [Member] \| Option Pricing Model [Member] \| Market Yields/Discount Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.0850	0.0875
Development Property Investments [Member] \| Maximum [Member] \| Option Pricing Model [Member] \| Exit Date [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	5.94	6.69
Development Property Investments [Member] \| Maximum [Member] \| Option Pricing Model [Member] \| Capitalization Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.0550	0.0575
Development Property Investments [Member] \| Weighted Average [Member] \| Income Approach Analysis [Member] \| Market Yields/Discount Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	0.0810	0.0839
Development Property Investments [Member] \| Weighted Average [Member] \| Income Approach Analysis [Member] \| Exit Date [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	3.65	3.40
Development Property Investments [Member] \| Weighted Average [Member] \| Option Pricing Model [Member] \| Volatility [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs \| $	0.7851	0.7324
Development Property Investments [Member] \| Weighted Average [Member] \| Option Pricing Model [Member] \| Market Yields/Discount Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs \| $	0.0843	0.0846
Development Property Investments [Member] \| Weighted Average [Member] \| Option Pricing Model [Member] \| Exit Date [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs	3.65	3.40
Development Property Investments [Member] \| Weighted Average [Member] \| Option Pricing Model [Member] \| Capitalization Rate [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Development property investments and bridge investments, unobservable inputs \| $	0.0543	0.0546
Development Property Investments [Member] \| Loan Investments [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Percentage of completion of construction	40.00%	40.00%
Thirty Eight Development Properties [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Percentage of completion of construction		40.00%
Thirty Eight Development Properties [Member] \| Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Percentage of completion of construction		100.00%
Twenty Development Properties [Member] \| Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Percentage of completion of construction	40.00%
Twenty Development Properties [Member] \| Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Percentage of completion of construction	100.00%

Jernigan Capital, Inc. 10-Q