Segment and Nonregulated Business Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 reportable_segment subsidiaries		Dec. 31, 2011		Dec. 31, 2010
Segment Reporting Information [Line Items]
Number of Subsidiaries											4
Operating revenue	$ 62,449	[1]	$ 82,374	$ 65,575	$ 51,149	$ 62,338	[1]	$ 73,914	$ 59,007	$ 43,696	$ 261,547		$ 238,955		$ 215,638
Utilities Operating Expense											206,250		184,564		177,563
Operating Income (Loss)	14,110	[1]	20,877	13,585	6,725	16,520	[1]	18,486	13,784	5,601	55,297		54,391		38,075
Net income	5,924	[1]	10,084	5,201	1,109	6,602	[1]	8,215	5,451	610	22,318		20,878		24,406
Depreciation and amortization											33,098		31,193		28,331
Provision for income taxes											15,542		14,566		16,740
Assets	1,087,499					1,038,810					1,087,499		1,038,810
Number of Reportable Segments											2
SJW Corp. [Member]
Segment Reporting Information [Line Items]
Operating revenue											261,547		238,955		215,638
Utilities Operating Expense											206,250		184,564		177,563
Operating Income (Loss)											55,297		54,391		38,075
Net income											22,318		20,878		24,406
Depreciation and amortization											33,098		31,193		28,331
Interest Expense											20,185		19,675		17,683
Provision for income taxes											15,542		14,566		16,740
Assets	1,087,499					1,038,810					1,087,499		1,038,810		935,362
Regulated [Member] | Water Utility Services [Member]
Segment Reporting Information [Line Items]
Operating revenue											251,032		229,411		207,432
Utilities Operating Expense											197,893		175,812		164,976
Operating Income (Loss)											53,139		53,599		42,456
Net income											22,811		21,970		16,818
Depreciation and amortization											31,085		29,136		26,319
Interest Expense											16,499		16,741		15,917
Provision for income taxes											15,678		15,387		11,496
Assets	991,866					917,580					991,866		917,580		844,364
Regulated [Member] | SJW Corp. [Member]
Segment Reporting Information [Line Items]
Operating revenue											251,032		229,411		207,432
Utilities Operating Expense											197,893		175,812		164,976
Operating Income (Loss)											53,139		53,599		42,456
Net income											22,811		21,970		16,818
Depreciation and amortization											31,085		29,136		26,319
Interest Expense											16,499		16,741		15,917
Provision for income taxes											15,678		15,387		11,496
Assets	991,866					917,580					991,866		917,580		844,364
Nonregulated [Member] | Water Utility Services [Member]
Segment Reporting Information [Line Items]
Operating revenue											5,523		4,935		4,646
Utilities Operating Expense											4,043		3,481		3,139
Operating Income (Loss)											1,480		1,454		1,507
Net income											707		765		846
Depreciation and amortization											360		360		347
Interest Expense											0		0		0
Provision for income taxes											581		571		600
Assets	13,245					11,668					13,245		11,668		9,849
Nonregulated [Member] | Real Estate Services [Member]
Segment Reporting Information [Line Items]
Operating revenue											4,992		4,609		3,560
Utilities Operating Expense											3,379		3,240		6,858
Operating Income (Loss)											1,613		1,369		(3,298)
Net income											244		(407)		(3,166)
Depreciation and amortization											1,653		1,697		1,665
Interest Expense											1,511		1,833		1,760
Provision for income taxes											374		(296)		(2,176)
Assets	74,903					80,097					74,903		80,097		81,361
Nonregulated [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Operating revenue											0	[2]	0	[2]	0	[2]
Utilities Operating Expense											935	[2]	2,031	[2]	2,590	[2]
Operating Income (Loss)											(935)	[2]	(2,031)	[2]	(2,590)	[2]
Net income											(1,444)	[2]	(1,450)	[2]	9,908	[2]
Depreciation and amortization											0	[2]	0	[2]	0	[2]
Interest Expense											2,175	[2]	1,101	[2]	6	[2]
Provision for income taxes											(1,091)	[2]	(1,096)	[2]	6,820	[2]
Assets	7,485	[2]				29,465	[2]				7,485	[2]	29,465	[2]	(212)	[2]
Nonregulated [Member] | SJW Corp. [Member]
Segment Reporting Information [Line Items]
Operating revenue											10,515		9,544		8,206
Utilities Operating Expense											8,357		8,752		12,587
Operating Income (Loss)											2,158		792		(4,381)
Net income											(493)		(1,092)		7,588
Depreciation and amortization											2,013		2,057		2,012
Interest Expense											3,686		2,934		1,766
Provision for income taxes											(136)		(821)		5,244
Assets	$ 95,633					$ 121,230					$ 95,633		$ 121,230		$ 90,998

[1] During the quarter ended December 31, 2012, the Company recorded revenues of $3,550 related to the recognition of certain San Jose Water Company balancing and memorandum accounts as the Company concluded that it was probable that these amounts would be collected. Of this amount, $240 represents a net over-collection of revenues generated during the quarter ended December 31, 2012 and $3,790 represents a net-under-collection of revenues which should have been recognized as revenue during the quarter ended September 30, 2012. See Note 1 of the Notes to the Consolidated Financial Statements for further discussion on balancing and memorandum accounts. During the quarter ended December 31, 2011, the Company recorded revenues of $5,740 related to the recognition of San Jose Water Company's MCRAM which was authorized for recovery by the CPUC on December 27, 2011.

[2] The “All Other” category is SJW Corp., on a stand-alone basis.