Consolidated Statements of Income and Comprehensive Income (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Statement [Abstract]
Operating revenue	$ 261,547	$ 238,955	$ 215,638
Production Costs:
Purchased water	66,106	54,317	43,557
Power	5,796	5,394	6,429
Groundwater extraction charges	23,940	20,997	26,614
Other production costs	11,445	11,345	10,702
Total production costs	107,287	92,053	87,302
Administrative and general	42,812	39,136	38,184
Maintenance	13,350	13,261	12,242
Property taxes and other non-income taxes	9,703	8,921	7,907
Depreciation and amortization	33,098	31,193	28,331
Impairment on real estate investment	0	0	3,597
Total operating expense	206,250	184,564	177,563
Operating income	55,297	54,391	38,075
Other (expense) income:
Interest on long-term debt	(18,662)	(17,799)	(15,676)
Mortgage and other interest expense	(1,523)	(1,876)	(2,007)
Gain on sale of California Water Service Group stock	0	0	18,966
Gain on sale of real estate investment	910	0	0
Dividend income	243	238	1,185
Other, net	1,595	490	603
Income before income taxes	37,860	35,444	41,146
Provision for income taxes	15,542	14,566	16,740
Net income	22,318	20,878	24,406
Other comprehensive income (loss):
Unrealized income (loss) on investment, net of taxes of $0 in 2012, $59 in 2011 and $30 in 2010	36	(85)	(44)
Reclassification adjustment for gain realized on investment, net of tax effect of $7,494	0	0	(10,784)
Comprehensive income	$ 22,354	$ 20,793	$ 13,578
Earnings per share
—Basic (in dollars per share)	$ 1.20	$ 1.12	$ 1.32
—Diluted (in dollars per share)	$ 1.18	$ 1.11	$ 1.30
Weighted average shares outstanding
—Basic	18,635,206	18,581,762	18,531,458
—Diluted	18,839,231	18,794,066	18,742,315