Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating revenue	$ 103,014	$ 169,254	$ 131,397	$ 98,149	$ 105,457	$ 146,349	$ 118,321	$ 90,272	$ 501,814	$ 460,399	$ 449,372
Operations:
Purchased water									142,570	125,930	121,695
Purchased power									30,053	29,577	28,252
Pump taxes									9,130	8,600	9,537
Administrative and general									85,758	75,276	75,243
Other									54,696	56,518	56,577
Maintenance									20,698	19,685	18,537
Depreciation and amortization									50,385	42,828	39,778
Income taxes									23,025	23,069	24,812
Property and other taxes									18,332	17,103	16,822
Total operating expenses									434,647	398,586	391,253
Net operating income	7,586	30,078	19,555	9,948	11,906	25,865	16,284	7,758	67,167	61,813	58,119
Other income and expenses:
Non-regulated revenue									16,160	15,993	18,190
Non-regulated expense									(15,822)	(12,312)	(12,452)
Gain on sale of non-utility property									62	22	560
Income tax (expense) on other income and expenses									(141)	(1,487)	(2,550)
Net other income									259	2,216	3,748
Interest expense:
Interest expense									32,455	27,936	24,394
Less: capitalized interest									(2,741)	(1,563)	(3,081)
Net interest expense									29,714	26,373	21,313
Net income	$ 1,868	$ 20,935	$ 12,190	$ 2,719	$ 4,871	$ 20,386	$ 10,381	$ 2,018	$ 37,712	$ 37,656	$ 40,554
Earnings per share:
Basic (in dollars per share)									$ 0.90	$ 0.90	$ 0.98
Diluted (in dollars per share)	$ 0.04	$ 0.50	$ 0.29	$ 0.07	$ 0.11	$ 0.49	$ 0.25	$ 0.05	$ 0.90	$ 0.90	$ 0.98
Weighted average number of common shares outstanding:
Basic (in shares)									41,762	41,612	41,490
Diluted (in shares)									41,772	41,638	41,532