RELATED PARTY TRANSACTIONS AND TRANSACTIONS WITH AFFILIATES (Details)								3 Months Ended		9 Months Ended
	Apr. 25, 2019 USD ($)	Apr. 01, 2019 USD ($)	Nov. 28, 2018 USD ($)	Oct. 04, 2018 USD ($)	Jun. 26, 2018 USD ($) $ / shares shares	Mar. 09, 2018 USD ($) $ / shares shares	Jan. 08, 2018 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) installment	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Base management fee percentage on first $500 million share capital							0.50%
Base management fee percentage in excess of $500 million share capital							0.25%
Annual reimbursement cap until 2019							$ 2,500,000
Annual reimbursement cap after 2019 until share capital exceeds of $500 million							$ 3,500,000
Renewal period of the agreement							2 years
Agreement Violation Termination Fee Includes An Amount Times Sum of Average Annual Base and Incentive Management Fee							3
Agreement Violation Termination Fee Includes An Amount Times Sum of Average Energy Capital Business Expense Reimbursement and Employee Cost Reimbursement Expense							1
Termination fee period							2 years
Aggregate cost of common stock shares issued					$ 4,300,000	$ 4,100,000
Consideration on disposal								$ 57,000,000		$ 57,000,000
Notes receivable								57,000,000		$ 57,000,000
Interest rate for note										5.00%
External management fees and reimbursable expenses								1,646,000	$ 1,059,000	$ 6,042,000	$ 5,762,000
Term of note receivable										7 years
Equity Method Investments								222,567,000		$ 222,567,000		$ 155,079,000
Investment in Debt Securities
Net proceeds from sale of affordable house property	$ 13,100,000
Hunt Companies [Member]
Loans and leases receivable from related party				$ 67,000,000
Quarterly amortization installments of note receivable										$ 3,350,000
Number of quarterly payments | installment										20
Interest income, related party								800,000	700,000	$ 2,500,000	2,100,000
Interest Receivable								800,000		800,000		0
Hunt Companies [Member] | External Management Fees and Expenses Reimbursement
Incentive fee							20.00%
External management fee, contract in excess for incentive fee.							7.00%
Incentive fee								0	0	0	0
External management fees and reimbursable expenses								1,600,000	1,100,000	6,000,000	5,800,000
Hunt Companies [Member] | External Management Fees and Expenses Reimbursement | External Manager [Member]
Management fees and expense reimbursements payable								$ 1,600,000		$ 1,600,000		$ 1,100,000
Hunt Companies [Member] | Investment in Debt Securities
Service fees waived by agent	900,000
Hunt Companies [Member] | Common shares in disposition
Shares issued (in shares) | shares					125,000	125,000
Shares issued					$ 4,300,000	$ 4,100,000
Purchase price (per share) | $ / shares					$ 34.00	$ 33.00
Hunt Companies [Member] | Common shares in disposition | Private Placement
Shares issued (in shares) | shares							250,000
Purchase price (per share) | $ / shares							$ 33.50
Hunt Companies [Member] | Investment in Debt Securities
Proceeds from redemption of bonds	$ 900,000
Solar Development Lending, LLC [Member]
Loan			$ 58,800,000						$ 104,000,000		$ 104,000,000
Percentage of loan amount contribution			20.00%
Solar Development Lending, LLC [Member] | Hunt Companies [Member]
Ownership interest		30.00%
Effective interest rate								17.30%		17.30%
Payments to Acquire Equity Method Investments		$ 11,300,000
Solar Development Lending, LLC [Member] | Hunt Companies [Member]
Percentage of loan amount contribution			30.00%
Solar Development Lending, LLC [Member] | Hunt Companies [Member] | Hunt Companies [Member]
Notes receivable amount								$ 20,000,000		$ 20,000,000
Solar Development Lending, LLC [Member] | Investment partner
Percentage of loan amount contribution			50.00%