SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details ) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 772,616	$ 765,704	$ 697,577
Regulatory balancing account revenue	73,815	25,205	96,730
Operating revenue	846,431	790,909	794,307
Non-regulated revenue	21,276	22,761	16,922
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	458,448	467,365	430,264
Business
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	153,570	144,565	125,819
Multiple residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	64,481	61,478	55,801
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26,622	26,569	29,088
Public authorities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	41,150	40,501	35,776
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	28,345	25,226	20,829
Operating and maintenance revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12,860	16,276	11,481
Other non-regulated revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5,774	3,741	3,043
Non-regulated revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18,634	20,017	14,524
Lease revenue	2,642	2,744	2,398
Non-regulated revenue	$ 21,276	$ 22,761	$ 16,922