Segment and Nonregulated Business Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012 subsidiaries		Sep. 30, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Number of Subsidiaries					4
Operating revenue	$ 82,374		$ 73,914		$ 199,098		$ 176,617
Operating expense	61,497		55,428		157,911		138,746
Operating income (loss)	20,877		18,486		41,187		37,871
Net income (loss)	10,084		8,215		16,394		14,276
Depreciation and amortization	8,288		7,803		24,922		23,389
Senior note, mortgage and other interest expense	5,063		5,120		15,188		14,533
Income tax expense (benefit) in net income	6,866		5,360		11,222		9,610
Assets	1,075,319		1,013,243		1,075,319		1,013,243		1,038,810
Water Utility Services [Member] | Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	79,333		71,013		191,059		169,355
Operating expense	59,239		52,898		151,586		132,044
Operating income (loss)	20,094		18,115		39,473		37,311
Net income (loss)	9,632		8,509		16,450		14,918
Depreciation and amortization	7,794		7,284		23,348		21,854
Senior note, mortgage and other interest expense	4,140		4,159		12,392		12,660
Income tax expense (benefit) in net income	6,557		5,582		11,261		10,105
Assets	980,086		885,053		980,086		885,053
Water Utility Services [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	1,855		1,704		4,351		3,879
Operating expense	1,233		1,145		3,140		2,650
Operating income (loss)	622		559		1,211		1,229
Net income (loss)	326		312		593		662
Depreciation and amortization	88		92		269		269
Senior note, mortgage and other interest expense	0		0		0		0
Income tax expense (benefit) in net income	246		227		479		486
Assets	13,100		11,561		13,100		11,561
Real Estate Services [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	1,186		1,197		3,688		3,383
Operating expense	805		844		2,478		2,493
Operating income (loss)	381		353		1,210		890
Net income (loss)	492		(80)		406		(347)
Depreciation and amortization	406		427		1,305		1,266
Senior note, mortgage and other interest expense	380		423		1,165		1,315
Income tax expense (benefit) in net income	338		(63)		279		(249)
Assets	74,116		80,895		74,116		80,895
All Other [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	0	[1]	0	[1]	0	[1]	0	[1]
Operating expense	220	[1]	541	[1]	707	[1]	1,559	[1]
Operating income (loss)	(220)	[1]	(541)	[1]	(707)	[1]	(1,559)	[1]
Net income (loss)	(366)	[1]	(526)	[1]	(1,055)	[1]	(957)	[1]
Depreciation and amortization	0	[1]	0	[1]	0	[1]	0	[1]
Senior note, mortgage and other interest expense	543	[1]	538	[1]	1,631	[1]	558	[1]
Income tax expense (benefit) in net income	(275)	[1]	(386)	[1]	(797)	[1]	(732)	[1]
Assets	8,017	[1]	35,734	[1]	8,017	[1]	35,734	[1]
SJW Corp. [Member] | Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	79,333		71,013		191,059		169,355
Operating expense	59,239		52,898		151,586		132,044
Operating income (loss)	20,094		18,115		39,473		37,311
Net income (loss)	9,632		8,509		16,450		14,918
Depreciation and amortization	7,794		7,284		23,348		21,854
Senior note, mortgage and other interest expense	4,140		4,159		12,392		12,660
Income tax expense (benefit) in net income	6,557		5,582		11,261		10,105
Assets	980,086		885,053		980,086		885,053
SJW Corp. [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	3,041		2,901		8,039		7,262
Operating expense	2,258		2,530		6,325		6,702
Operating income (loss)	783		371		1,714		560
Net income (loss)	452		(294)		(56)		(642)
Depreciation and amortization	494		519		1,574		1,535
Senior note, mortgage and other interest expense	923		961		2,796		1,873
Income tax expense (benefit) in net income	309		(222)		(39)		(495)
Assets	$ 95,233		$ 128,190		$ 95,233		$ 128,190

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