Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 440,986		$ 433,322
Total Regulatory Liabilities	208,539		211,413
Short-term portion of the regulatory assets	23,738		38,225
Short-term portion of the regulatory liabilities	1,602		4,462
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Total Regulatory Liabilities	192,055		194,501
HCBA
Regulatory Assets and Liabilities
Total Regulatory Liabilities	4,271		4,271
CEBA
Regulatory Assets and Liabilities
Total Regulatory Liabilities	1,556		2,742
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Total Regulatory Liabilities	90		211
Tax accounting memorandum account
Regulatory Assets and Liabilities
Total Regulatory Liabilities	668		806
Cost of capital memorandum account
Regulatory Assets and Liabilities
Total Regulatory Liabilities	15		151
1,2,3 trichloropropane (TCP) settlement proceeds
Regulatory Assets and Liabilities
Total Regulatory Liabilities	9,288		8,426
Other regulatory liabilities
Regulatory Assets and Liabilities
Total Regulatory Liabilities	596		305
Pension and retiree group health
Regulatory Assets and Liabilities
Total Regulatory Assets	207,992		208,321
Property-related temporary differences (tax benefits flowed through to customers)
Regulatory Assets and Liabilities
Total Regulatory Assets	106,306		104,931
Other accrued benefits
Regulatory Assets and Liabilities
Total Regulatory Assets	21,444		20,030
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Total Regulatory Assets	27,621		25,465
Asset retirement obligations, net
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 20,529		19,567
Interim rates long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 4,642		4,642
Tank coating
Regulatory Assets and Liabilities
Recovery Period	10 years
Total Regulatory Assets	$ 14,599		13,535
Recoverable property losses
Regulatory Assets and Liabilities
Recovery Period	10 years
Total Regulatory Assets	$ 4,707		5,000
PCBA
Regulatory Assets and Liabilities
Recovery Period	1 year
Total Regulatory Assets	$ 21,465		21,465
Other components of net periodic benefit cost
Regulatory Assets and Liabilities
Total Regulatory Assets	5,969		5,145
Other regulatory assets
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 5,712		$ 5,221
Minimum | Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	1 year
Maximum | Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Recovery Period	2 years
Forecast
Regulatory Assets and Liabilities
Amount of construction work in process included in rate base		$ 148,000
Forecast | 2019-2021 | Minimum
Regulatory Assets and Liabilities
Amount of construction work in process included in rate base		609,000
Investments in Capital Improvements		809,000
Forecast | 2019-2021 | Maximum
Regulatory Assets and Liabilities
Amount of construction work in process included in rate base		628,000
Investments in Capital Improvements		828,000
Forecast | 2018
Regulatory Assets and Liabilities
Amount of construction work in process included in rate base		$ 200,000