SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Lessor, Lease, Description [Line Items]
Maximum collection period in which deferred net WRAM and MCBA revenues and associated costs will be recognized	24 months
Revenue from contracts with customers	$ 772,616	$ 765,704	$ 697,577
Optional lease renewal term	15 years
Provision for depreciation expressed as a percentage of the aggregate depreciable asset balances	2.90%	2.96%	2.94%
Proceeds collected through a surcharge on certain customers' bills	$ 400	$ 400
Goodwill impairment	0	0	$ 0
Amortization of debt premium and expenses	369	366	$ 412
Total refunds	$ 199,832	$ 198,086
Refund period	40 years
Insurance Programs
Lessor, Lease, Description [Line Items]
Revenue from contracts with customers	$ 2,700
Minimum
Lessor, Lease, Description [Line Items]
Term of contract	5 years
Maximum
Lessor, Lease, Description [Line Items]
Term of contract	10 years