REGULATORY ASSETS AND LIABILITIES - Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Regulatory Assets and Liabilities
Regulatory Assets	$ 357,406	$ 257,621
Regulatory Liabilities	814,551	683,717
Cost of removal
Regulatory Assets and Liabilities
Regulatory Liabilities	483,108	447,356
Pension and retiree group health
Regulatory Assets and Liabilities
Regulatory Liabilities	174,708	88,728
Future tax benefits due to customers
Regulatory Assets and Liabilities
Regulatory Liabilities	106,184	118,051
Other components of net periodic benefit cost
Regulatory Assets and Liabilities
Regulatory Liabilities	18,287	10,348
PCBA
Regulatory Assets and Liabilities
Regulatory Liabilities	14,143	8,972
ICBA
Regulatory Assets and Liabilities
Regulatory Liabilities	6,003	0
HCBA
Regulatory Assets and Liabilities
Regulatory Liabilities	3,630	3,242
CEBA
Regulatory Assets and Liabilities
Regulatory Liabilities	3,294	1,200
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Regulatory Liabilities	3,064	2,071
RSF regulatory liability
Regulatory Assets and Liabilities
Regulatory Liabilities	0	2,116
Other regulatory liabilities
Regulatory Assets and Liabilities
Regulatory Liabilities	2,130	1,633
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Regulatory Assets	178,279	158,486
IRMA long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory Assets	46,278	3,430
Asset retirement obligations, net
Regulatory Assets and Liabilities
Regulatory Assets	28,883	26,686
Other accrued benefits
Regulatory Assets and Liabilities
Regulatory Assets	25,439	25,363
Tank coating
Regulatory Assets and Liabilities
Regulatory Assets	21,477	19,602
MWRAM long-term regulatory asset
Regulatory Assets and Liabilities
Regulatory Assets	$ 16,353	0
Customer assistance program (CAP) and Rate support fund (RSF) accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Regulatory Assets	$ 9,910	2,459
General district balancing account receivable
Regulatory Assets and Liabilities
Regulatory Assets	$ 9,393	390
ICBA
Regulatory Assets and Liabilities
Recovery Period	1 year
Regulatory Assets	$ 8,251	0
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory Assets	3,633	10,738
Recoverable property losses
Regulatory Assets and Liabilities
Regulatory Assets	2,633	3,121
PCBA
Regulatory Assets and Liabilities
Regulatory Assets	0	4,182
Other regulatory assets
Regulatory Assets and Liabilities
Regulatory Assets	$ 6,877	$ 3,164
Minimum | MWRAM long-term regulatory asset
Regulatory Assets and Liabilities
Recovery Period	1 year
Maximum | MWRAM long-term regulatory asset
Regulatory Assets and Liabilities
Recovery Period	2 years