Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Consolidated Statements of Income
Operating revenue	$ 133,700	$ 184,404	$ 154,555	$ 111,444	$ 121,530	$ 178,135	$ 143,552	$ 116,749	$ 584,103	$ 559,966	$ 501,814
Operations:
Purchased water									183,046	161,336	142,570
Purchased power									32,220	31,027	30,053
Pump taxes									10,795	10,336	9,130
Administrative and general									98,055	93,927	85,758
Other									69,738	77,104	54,696
Maintenance									17,368	19,142	20,698
Depreciation and amortization									58,320	54,668	50,385
Income taxes									19,047	19,356	23,025
Property and other taxes									21,509	19,227	18,332
Total operating expenses									510,098	486,123	434,647
Net operating income	11,648	35,804	20,783	5,770	11,253	36,361	19,622	6,607	74,005	73,843	67,167
Other income and expenses:
Non-regulated revenue									14,795	16,686	16,160
Non-regulated expense									(11,265)	(11,553)	(15,822)
Gain on sale of non-utility property										84	62
Income tax (expense) on other income and expenses									(1,422)	(2,096)	(141)
Net other income									2,108	3,121	259
Interest expense:
Interest expense									30,897	31,537	32,455
Less: capitalized interest									(2,038)	(3,401)	(2,741)
Net interest expense									28,859	28,136	29,714
Net income									$ 47,254	$ 48,828	$ 37,712
Earnings per share:
Basic (in dollars per share)									$ 1.02	$ 1.17	$ 0.90
Diluted (in dollars per share)	$ 0.12	$ 0.61	$ 0.28	$ (0.03)	$ 0.12	$ 0.71	$ 0.31	$ 0.03	$ 1.02	$ 1.17	$ 0.90
Weighted average number of common shares outstanding:
Basic (in shares)									46,384	41,892	41,762
Diluted (in shares)									46,417	41,892	41,772