Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	$ 167,467	$ 171,772	$ 284,877	$ 306,026
Regulatory balancing account revenue	11,564	3,166	20,265	3,465
Total operating revenue	179,031	174,938	$ 305,142	309,491
Maximum collection period in which deferred net WRAM and MCBA revenues and associated costs will be recognized			24 months
Total non-regulated revenue	$ 5,130	4,845	$ 10,031	9,264
Lessor operating lease renewal term	15 years		15 years
2019	$ 3,095		$ 3,095
2020	2,499		2,499
2021	1,827		1,827
2022	1,031		1,031
2023	554		554
Thereafter	872		872
Cash and cash equivalents	54,560		54,560			$ 47,176
Restricted cash (included in taxes, prepaid expenses and other assets)	520		520			539
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	55,080	34,265	55,080	34,265		$ 47,715	$ 95,352
Other assets	14,241		14,241
Operating lease liability	$ 14,206		$ 14,206
ASU 2016-02
Summary of Significant Accounting Policies [Line Items]
Operating lease liability					$ 13,800
Minimum
Summary of Significant Accounting Policies [Line Items]
Lessor operating lease term	5 years		5 years
Maximum
Summary of Significant Accounting Policies [Line Items]
Lessor operating lease term	10 years		10 years
Regulated water and wastewater services
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	$ 167,467	171,772	$ 284,877	306,026
Total operating revenue	179,031	174,938	305,142	309,491
Operating and maintenance revenue
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	3,273	2,297	6,319	5,462
Other non-regulated revenue
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	1,267	1,981	2,563	2,724
Non-regulated revenue
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	4,540	4,278	8,882	8,186
Lease revenue	590	567	1,149	1,078
Total non-regulated revenue	5,130	4,845	10,031	9,264
Residential
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	107,349	109,849	191,609	201,167
Business
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	31,706	32,125	57,186	59,182
Industrial
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	7,524	7,941	14,788	15,520
Public authorities
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers	7,613	8,251	12,084	13,695
Other (a)
Summary of Significant Accounting Policies [Line Items]
Revenue from contracts with customers			$ 9,210	$ 16,462
Other	$ 13,275	$ 13,606