Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Income
Operating revenue	$ 121,530	$ 178,135	$ 143,552	$ 116,749	$ 103,014	$ 169,254	$ 131,397	$ 98,149	$ 559,966	$ 501,814	$ 460,399
Operations:
Purchased water									161,336	142,570	125,930
Purchased power									31,027	30,053	29,577
Pump taxes									10,336	9,130	8,600
Administrative and general									93,927	85,758	75,276
Other									77,104	54,696	56,518
Maintenance									19,142	20,698	19,685
Depreciation and amortization									54,668	50,385	42,828
Income taxes									19,356	23,025	23,069
Property and other taxes									19,227	18,332	17,103
Total operating expenses									486,123	434,647	398,586
Net operating income	11,253	36,361	19,622	6,607	7,586	30,078	19,555	9,948	73,843	67,167	61,813
Other income and expenses:
Non-regulated revenue									16,686	16,160	15,993
Non-regulated expense									(11,553)	(15,822)	(12,312)
Gain on sale of non-utility property									84	62	22
Income tax (expense) on other income and expenses									(2,096)	(141)	(1,487)
Net other income									3,121	259	2,216
Interest expense:
Interest expense									31,537	32,455	27,936
Less: capitalized interest									(3,401)	(2,741)	(1,563)
Net interest expense									28,136	29,714	26,373
Net income									$ 48,828	$ 37,712	$ 37,656
Earnings per share:
Basic (in dollars per share)									$ 1.17	$ 0.90	$ 0.90
Diluted (in dollars per share)	$ 0.12	$ 0.71	$ 0.31	$ 0.03	$ 0.04	$ 0.50	$ 0.29	$ 0.07	$ 1.17	$ 0.90	$ 0.90
Weighted average number of common shares outstanding:
Basic (in shares)									41,892	41,762	41,612
Diluted (in shares)									41,892	41,772	41,638