Segment and Nonregulated Business Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 subsidiaries		Mar. 31, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of Subsidiaries	4
Operating revenue	$ 50,139		$ 51,149
Operating expense	44,366		44,424
Operating income (loss)	5,773		6,725
Net income (loss)	1,317		1,109
Depreciation and amortization	8,816		8,308
Senior note, mortgage and other interest expense	5,022		5,075
Income tax expense (benefit) in net income	930		799
Assets	1,098,691		1,042,444		1,087,499
Water Utility Services [Member] | Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	47,798		48,824
Operating expense	41,625		42,350
Operating income (loss)	6,173		6,474
Net income (loss)	1,600		1,454
Depreciation and amortization	8,322		7,786
Senior note, mortgage and other interest expense	4,152		4,137
Income tax expense (benefit) in net income	922		1,046
Assets	1,004,441		942,540
Water Utility Services [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	1,086		1,074
Operating expense	1,682		748
Operating income (loss)	(596)		326
Net income (loss)	(508)		160
Depreciation and amortization	88		91
Senior note, mortgage and other interest expense	0		0
Income tax expense (benefit) in net income	(144)		125
Assets	16,171		12,301
Real Estate Services [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	1,255		1,251
Operating expense	810		846
Operating income (loss)	445		405
Net income (loss)	636		(35)
Depreciation and amortization	406		431
Senior note, mortgage and other interest expense	320		394
Income tax expense (benefit) in net income	460		(24)
Assets	69,492		79,238
All Other [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	0	[1]	0	[1]
Operating expense	249	[1]	480	[1]
Operating income (loss)	(249)	[1]	(480)	[1]
Net income (loss)	(411)	[1]	(470)	[1]
Depreciation and amortization	0	[1]	0	[1]
Senior note, mortgage and other interest expense	550	[1]	544	[1]
Income tax expense (benefit) in net income	(308)	[1]	(348)	[1]
Assets	8,587	[1]	8,365	[1]
SJW Corp. [Member] | Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	47,798		48,824
Operating expense	41,625		42,350
Operating income (loss)	6,173		6,474
Net income (loss)	1,600		1,454
Depreciation and amortization	8,322		7,786
Senior note, mortgage and other interest expense	4,152		4,137
Income tax expense (benefit) in net income	922		1,046
Assets	1,004,441		942,540
SJW Corp. [Member] | Nonregulated [Member]
Segment Reporting Information [Line Items]
Operating revenue	2,341		2,325
Operating expense	2,741		2,074
Operating income (loss)	(400)		251
Net income (loss)	(283)		(345)
Depreciation and amortization	494		522
Senior note, mortgage and other interest expense	870		938
Income tax expense (benefit) in net income	8		(247)
Assets	$ 94,250		$ 99,904

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