SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessor, Lease, Description [Line Items]
Maximum collection period in which deferred net WRAM and MCBA revenues and associated costs will be recognized	24 months
Optional lease renewal term	15 years
Provision for depreciation expressed as a percentage of the aggregate depreciable asset balances	2.96%	2.94%	2.96%
Proceeds collected through a surcharge on certain customers' bills	$ 500	$ 600
Amortization of debt premium and expenses	366	412	$ 744
Total refunds	$ 198,086	$ 195,625
Refund period	40 years
Minimum
Lessor, Lease, Description [Line Items]
Term of contract	5 years
Maximum
Lessor, Lease, Description [Line Items]
Term of contract	10 years