FAIR VALUE - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)	Oct. 16, 2018	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		$ 2,135,000	$ 2,135,000
Long-term debt, fair value		129,961,000	127,724,000
Acquisition liability		838,000	838,000
Fair value, of net assets (liabilities)		133,777,000	133,969,000
Organizational costs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Growth premium payable for each new meter installed	$ 750	750
Period for maximum payout of growth premium after first meter install (in years)	10 years
Period for maximum payout of growth premium after acquisition date (in years)	20 years
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		2,135,000	2,135,000
Long-term debt, fair value		0	0
Acquisition liability		0	0
Assets		2,135,000	2,135,000
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		0	0
Long-term debt, fair value		129,961,000	127,724,000
Acquisition liability		0	0
Fair value, of net assets (liabilities)		130,804,000	130,996,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		0	0
Long-term debt, fair value		0	0
Acquisition liability		838,000	838,000
Fair value, of net assets (liabilities)		838,000	838,000
Hook Up Fee Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		53,000	2,482,000
Hook Up Fee Funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		0	0
Hook Up Fee Funds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		53,000	2,482,000
Hook Up Fee Funds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		0	0
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		790,000	790,000
Certificates of Deposit | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		0	0
Certificates of Deposit | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		790,000	790,000
Certificates of Deposit | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents		$ 0	$ 0