SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details ) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 790,334	$ 772,616	$ 765,704
Regulatory balancing account revenue	4,298	73,815	25,205
Operating revenue	794,632	846,431	790,909
Non-regulated revenue	18,509	21,276	22,761
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	463,417	458,448	467,365
Business
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	159,050	153,570	144,565
Multiple residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	67,703	64,481	61,478
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	28,055	26,622	26,569
Public authorities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	40,811	41,150	40,501
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	31,298	28,345	25,226
Operating and maintenance revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12,499	12,860	16,276
Other non-regulated revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,506	5,774	3,741
Non-regulated revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16,005	18,634	20,017
Lease revenue	2,504	2,642	2,744
Non-regulated revenue	$ 18,509	$ 21,276	$ 22,761