Financial Statement Schedule - Condensed Balance Sheets (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 11,114	$ 9,723	$ 12,344	$ 12,119
Other current assets	8,593	6,146
Total current assets	190,714	198,389
Other assets
Other	28,893	8,056
Total other assets	977,768	962,868
Total assets	4,658,309	4,345,067
Stockholders’ equity:
Common stock, $0.001 par value; authorized 70,000,000 shares in 2024 and 2023; issued and outstanding 33,629,169 shares in 2024 and 32,023,004 shares in 2023	34	32
Additional paid-in capital	827,796	736,191
Retained earnings	537,184	495,383
Accumulated other comprehensive income	1,960	1,791
Total stockholders’ equity	1,366,974	1,233,397	1,110,868	1,034,519
Long-term debt, less current portion	1,706,904	1,526,699
Total capitalization	3,073,878	2,760,096
Current liabilities:
Line of credit	119,124	171,500
Accounts payable	56,256	46,121
Accrued interest	17,476	15,816
Other current liabilities	23,236	20,795
Total current liabilities	261,173	342,974
Deferred income taxes	276,043	238,528
Other noncurrent liabilities	22,298	22,492
Total capitalization and liabilities	$ 4,658,309	$ 4,345,067
Common stock, par value (usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	70,000,000	70,000,000
Common stock, shares issued (in shares)	33,629,169	32,023,004
Common stock, shares outstanding (in shares)	33,629,169	32,023,004
SJW Group
Assets
Investments in subsidiaries	$ 1,877,922	$ 1,753,250
Current assets:
Cash and cash equivalents	1,306	868	$ 5,142	$ 2,859
Intercompany receivables	1,473	2,239
Intercompany notes receivable	74,119	69,746
Other current assets	1,177	243
Total current assets	78,075	73,096
Other assets
Other	222	193
Total other assets	222	193
Total assets	1,956,219	1,826,539
Stockholders’ equity:
Common stock, $0.001 par value; authorized 70,000,000 shares in 2024 and 2023; issued and outstanding 33,629,169 shares in 2024 and 32,023,004 shares in 2023	34	32
Additional paid-in capital	827,796	736,191
Retained earnings	537,184	495,383
Accumulated other comprehensive income	1,960	1,791
Total stockholders’ equity	1,366,974	1,233,397
Long-term debt, less current portion	557,430	557,028
Total capitalization	1,924,404	1,790,425
Current liabilities:
Line of credit	3,000	10,000
Intercompany payables	2,210	0
Intercompany notes payable	0	1,726
Accounts payable	1,588	0
Accrued interest	3,224	3,255
Income tax payable	16,871	16,427
Other current liabilities	765	629
Total current liabilities	27,658	32,037
Deferred income taxes	2,488	3,099
Other noncurrent liabilities	1,669	978
Total capitalization and liabilities	$ 1,956,219	$ 1,826,539