SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details ) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 963,695	$ 905,623	$ 790,334
Regulatory balancing account revenue	36,445	131,183	4,298
Operating revenue	1,000,140	1,036,806	794,632
Non-regulated revenue	20,776	20,628	18,509
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	567,274	538,234	463,417
Business
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	192,668	180,032	159,050
Multiple residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	83,997	76,835	67,703
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30,962	30,399	28,055
Public authorities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	54,681	49,162	40,811
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	34,113	30,961	31,298
Contract operating and maintenance revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13,734	13,818	12,499
Other non-regulated revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,708	4,400	3,506
Non-regulated revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18,442	18,218	16,005
Lease revenue	2,334	2,410	2,504
Non-regulated revenue	$ 20,776	$ 20,628	$ 18,509