Long-Term Debt Long-term Debt Schedule (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt	$ 1,292,586	$ 435,000
Unamortized debt premium, net	25,020	0
Unamortized Debt Issuance Expense	11,737	3,576
Current portion	22,272	0
Long-term debt, less current portion	1,283,597	431,424
SJW Group [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 560,000	50,000
SJW Group [Member] \| Senior Notes [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	4.35%
San Jose Water Company [Member] \| California Pollution Control Financing Authority Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt	$ 450,000	370,000
San Jose Water Company [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 330,000	250,000
San Jose Water Company [Member] \| Senior Notes [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	4.29%
San Jose Water Company [Member] \| Senior Notes [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	9.45%
San Jose Water Company [Member] \| Public Utility, Bonds [Member] \| California Pollution Control Financing Authority Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt	$ 120,000	120,000
San Jose Water Company [Member] \| Public Utility, Bonds [Member] \| California Pollution Control Financing Authority Revenue Bonds [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	4.75%
San Jose Water Company [Member] \| Public Utility, Bonds [Member] \| California Pollution Control Financing Authority Revenue Bonds [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	5.10%
Connecticut Water Service, Inc. [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 23,935	0
Connecticut Water Service, Inc. [Member] \| Notes Payable to Banks [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	4.09%
Connecticut Water Service, Inc. [Member] \| Notes Payable to Banks [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	4.15%
Connecticut Water Company [Member]
Debt Instrument [Line Items]
Long-term debt	$ 198,646	0
Connecticut Water Company [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 35,000	0
Stated interest rates	3.53%
Connecticut Water Company [Member] \| Public Utility, Bonds [Member] \| Connecticut Innovations Revenue Bonds, Variable Rate [Member]
Debt Instrument [Line Items]
Long-term debt	$ 22,050	0
Connecticut Water Company [Member] \| Public Utility, Bonds [Member] \| Connecticut Innovations Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt	$ 22,506	0
Stated interest rates	5.00%
Connecticut Water Company [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 119,090	0
Connecticut Water Company [Member] \| Notes Payable to Banks [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	3.16%
Connecticut Water Company [Member] \| Notes Payable to Banks [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	4.75%
SJWTX, Inc. [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 15,000	15,000
Stated interest rates	6.27%
Maine Water Company [Member]
Debt Instrument [Line Items]
Long-term debt	$ 38,032	0
Maine Water Company [Member] \| Public Utility, Bonds [Member] \| State Revolving Fund Loans [Member]
Debt Instrument [Line Items]
Long-term debt	$ 16,032	0
Maine Water Company [Member] \| Public Utility, Bonds [Member] \| State Revolving Fund Loans [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	0.00%
Maine Water Company [Member] \| Public Utility, Bonds [Member] \| State Revolving Fund Loans [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	2.58%
Maine Water Company [Member] \| Public Utility, Bonds [Member] \| First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Stated interest rates	8.95%
Maine Water Company [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 17,500	0
Maine Water Company [Member] \| Notes Payable to Banks [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rates	4.18%
Maine Water Company [Member] \| Notes Payable to Banks [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rates	5.51%
Maine Water Company [Member] \| Mortgages [Member] \| First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Long-term debt	$ 4,500	0
Heritage Valley Water Company [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term debt	$ 4,164	0
Stated interest rates	4.75%
Avon Water Company [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,809	$ 0
Stated interest rates	3.05%

Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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