Segment and Nonregulated Business Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenue	$ 65,575		$ 59,007		$ 116,724		$ 102,703
Operating expense	51,990		45,223		96,414		83,318
Operating income (loss)	13,585		13,784		20,310		19,385
Net income (loss)	5,201		5,451		6,310		6,061
Depreciation and amortization	8,326		7,792		16,634		15,586
Senior note, mortgage and other interest expense	5,050		4,682		10,125		9,413
Income tax expense (benefit) in net income	3,557		3,817		4,356		4,250
Assets	1,055,247		1,000,314		1,055,247		1,000,314		1,038,810
Regulated [Member] | Water Utility Services [Member]
Segment Reporting Information [Line Items]
Operating revenue	62,902		56,660		111,726		98,342
Operating expense	49,997		43,076		92,347		79,146
Operating income (loss)	12,905		13,584		19,379		19,196
Net income (loss)	5,364		5,549		6,818		6,409
Depreciation and amortization	7,768		7,282		15,554		14,570
Senior note, mortgage and other interest expense	4,115		4,235		8,252		8,501
Income tax expense (benefit) in net income	3,658		3,905		4,704		4,523
Assets	954,955		865,296		954,955		865,296
Regulated [Member] | SJW Corp. [Member]
Segment Reporting Information [Line Items]
Operating revenue	62,902		56,660		111,726		98,342
Operating expense	49,997		43,076		92,347		79,146
Operating income (loss)	12,905		13,584		19,379		19,196
Net income (loss)	5,364		5,549		6,818		6,409
Depreciation and amortization	7,768		7,282		15,554		14,570
Senior note, mortgage and other interest expense	4,115		4,235		8,252		8,501
Income tax expense (benefit) in net income	3,658		3,905		4,704		4,523
Assets	954,955		865,296		954,955		865,296
Nonregulated [Member] | Water Utility Services [Member]
Segment Reporting Information [Line Items]
Operating revenue	1,422		1,268		2,496		2,175
Operating expense	1,159		807		1,907		1,505
Operating income (loss)	263		461		589		670
Net income (loss)	107		251		267		350
Depreciation and amortization	90		90		181		177
Senior note, mortgage and other interest expense	0		0		0		0
Income tax expense (benefit) in net income	108		177		233		259
Assets	13,016		11,374		13,016		11,374
Nonregulated [Member] | Real Estate Services [Member]
Segment Reporting Information [Line Items]
Operating revenue	1,251		1,079		2,502		2,186
Operating expense	827		859		1,673		1,649
Operating income (loss)	424		220		829		537
Net income (loss)	(51)		(147)		(86)		(267)
Depreciation and amortization	468		420		899		839
Senior note, mortgage and other interest expense	391		427		785		892
Income tax expense (benefit) in net income	(35)		(102)		(59)		(186)
Assets	79,290		81,198		79,290		81,198
Nonregulated [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Operating revenue	0	[1]	0	[1]	0	[1]	0	[1]
Operating expense	7	[1]	481	[1]	487	[1]	1,018	[1]
Operating income (loss)	(7)	[1]	(481)	[1]	(487)	[1]	(1,018)	[1]
Net income (loss)	(219)	[1]	(202)	[1]	(689)	[1]	(431)	[1]
Depreciation and amortization	0	[1]	0	[1]	0	[1]	0	[1]
Senior note, mortgage and other interest expense	544	[1]	20	[1]	1,088	[1]	20	[1]
Income tax expense (benefit) in net income	(174)	[1]	(163)	[1]	(522)	[1]	(346)	[1]
Assets	7,986	[1]	42,446	[1]	7,986	[1]	42,446	[1]
Nonregulated [Member] | SJW Corp. [Member]
Segment Reporting Information [Line Items]
Operating revenue	2,673		2,347		4,998		4,361
Operating expense	1,993		2,147		4,067		4,172
Operating income (loss)	680		200		931		189
Net income (loss)	(163)		(98)		(508)		(348)
Depreciation and amortization	558		510		1,080		1,016
Senior note, mortgage and other interest expense	935		447		1,873		912
Income tax expense (benefit) in net income	(101)		(88)		(348)		(273)
Assets	$ 100,292		$ 135,018		$ 100,292		$ 135,018

[1] The “All Other” category includes the accounts of SJW Corp. on a stand-alone basis.