REVENUE - Narrative (Details) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Apr. 01, 2018
Disaggregation Of Revenue [Line Items]
Cumulative effect of initially applying new standards	$ 400,000								$ 400,000
Total revenue	22,443,000	$ 16,291,000	$ 13,198,000	$ 13,822,000	$ 15,057,000	$ 17,263,000	$ 15,422,000	$ 12,558,000	$ 65,754,000	$ 60,300,000	$ 70,211,000
Percentage of contract for sale equal monthly progress payments									90.00%
Proceeds from sale of revenue earned but not billed									$ 6,900,000
Gain (loss) on sale of revenue earned but not billed									$ (300,000)
Revenue, Practical Expedient, Initial Application and Transition, Nondisclosure of Transaction Price Allocation to Remaining Performance Obligation [true false]									true
Revenue, Practical Expedient, Financing Component [true false]									true
Unbilled accounts receivable	$ 700,000								$ 700,000			$ 600,000
Contract liabilities									48,000
Change in contract asset reclassified to accounts receivable									0
Change in contract liability									0
Light fixture sales-type lease
Disaggregation Of Revenue [Line Items]
Total revenue									3,400,000
Sale of tax credits
Disaggregation Of Revenue [Line Items]
Total revenue									200,000
Legacy solar facilities
Disaggregation Of Revenue [Line Items]
Total revenue									$ 100,000