Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated Statements of Income
Operating revenue	$ 137,384	$ 191,184	$ 158,416	$ 110,515	$ 133,700	$ 184,404	$ 154,555	$ 111,444	$ 597,499	$ 584,103	$ 559,966
Operations:
Purchased water									177,884	183,046	161,336
Purchased power									33,159	32,220	31,027
Pump taxes									12,898	10,795	10,336
Administrative and general									97,373	98,055	93,927
Other									65,807	69,738	77,104
Maintenance									19,854	17,368	19,142
Depreciation and amortization									61,217	58,320	54,668
Income taxes									26,727	19,047	19,356
Property and other taxes									20,733	21,509	19,227
Total operating expenses									515,652	510,098	486,123
Net operating income	16,569	40,834	23,292	1,152	11,648	35,804	20,783	5,770	81,847	74,005	73,843
Other income and expenses:
Non-regulated revenue									17,318	14,795	16,686
Non-regulated expenses									(14,285)	(11,265)	(11,553)
Gain on sale of non-utility property									51		84
Income tax (expense) on other income and expenses									(1,245)	(1,422)	(2,096)
Net other income									1,839	2,108	3,121
Interest expense:
Interest expense									28,483	30,897	31,537
Less: capitalized interest									(1,535)	(2,038)	(3,401)
Net interest expense									26,948	28,859	28,136
Net income									$ 56,738	$ 47,254	$ 48,828
Earnings per share:
Basic									$ 1.19	$ 1.02	$ 1.17
Diluted	$ 0.24	$ 0.70	$ 0.36	$ (0.11)	$ 0.12	$ 0.61	$ 0.28	$ (0.03)	$ 1.19	$ 1.02	$ 1.17
Weighted average shares outstanding:
Basic									47,791	46,384	41,892
Diluted									47,829	46,417	41,892