RELATED PARTY TRANSACTIONS AND TRANSACTIONS WITH AFFILIATES (Details)								3 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	Mar. 31, 2019 USD ($) installment	Mar. 31, 2018 USD ($)	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
Consideration, common stock shares issued | shares					125,000	125,000
Disposal Group, Consideration, Shares Transfered, Price per Share | $ / shares					$ 34.00	$ 33.00
Notes receivable								$ 57,000,000
Interest rate for note								5.00%
External management fees and reimbursable expenses								$ 2,268,000	$ 2,519,000
Term of note receivable								7 years
Equity Method Investments								$ 159,145,000		$ 155,079,000
Subsequent Events | Hunt
Ownership interest		30.00%
Investment in Partnerships (SDL)
Percentage of loan amount contribution			20.00%
Investment in Debt Securities | Subsequent Events
Net proceeds from sale of affordable house property	$ 13,100,000
Hunt
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	600,000
Interest Receivable								800,000		0
Hunt | 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
External management fees and reimbursable expenses								2,300,000	$ 2,500,000
Hunt | External Management Fees and Expenses Reimbursement | External Manager
Management fees and expense reimbursements payable								2,200,000		$ 1,100,000
Hunt | Investment in Partnerships (SDL)
Maximum potential loan contribution			$ 58,800,000					$ 58,800,000
Percentage of loan amount contribution			30.00%
Hunt | Investment in Debt Securities | Subsequent Events
Service fees waived by agent	900,000
Hunt | 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 | Common shares in disposition | Private Placement
Shares issued (in shares) | shares							250,000
Purchase price (per share) | $ / shares							$ 33.50
Solar Development Lending, LLC [Member]
Percentage of loan amount contribution			50.00%
Hunt | Investment in Debt Securities | Subsequent Events
Proceeds from redemption of bonds	$ 900,000
Solar Development Lending, LLC [Member] | Subsequent Events | Hunt
Ownership interest		30.00%
Payments to Acquire Equity Method Investments		$ 11,300,000