CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Operating revenue	$ 183,543	$ 191,184	$ 449,942	$ 460,115
Operations:
Water production costs	60,437	66,980	158,661	174,297
Administrative and general	30,737	23,765	85,069	72,702
Other operations	17,872	15,692	51,227	48,072
Maintenance	5,952	4,800	15,735	14,793
Depreciation and amortization	15,342	14,648	46,015	46,788
Income taxes	15,293	19,233	21,008	22,584
Property and other taxes	5,709	5,232	16,036	15,601
Total operating expenses	151,342	150,350	393,751	394,837
Net operating income	32,201	40,834	56,191	65,278
Other income and expenses:
Non-regulated revenue	3,814	4,409	10,540	12,163
Non-regulated expenses, net	(4,454)	(4,812)	(10,201)	(11,184)
Income tax benefit on other income and expenses	262	169	(131)	(391)
Net other loss	(378)	(234)	208	588
Interest expense:
Interest expense	7,201	7,221	21,331	21,373
Less: capitalized interest	(498)	(271)	(1,472)	(851)
Net interest expense	6,703	6,950	19,859	20,522
Net Income	$ 25,120	$ 33,650	$ 36,540	$ 45,344
Earnings per share:
Basic (in dollars per share)	$ 0.52	$ 0.70	$ 0.76	$ 0.95
Diluted (in dollars per share)	$ 0.52	$ 0.70	$ 0.76	$ 0.95
Weighted average shares outstanding:
Basic (in shares)	47,878	47,803	47,861	47,787
Diluted (in shares)	47,887	47,840	47,877	47,825
Dividends declared per share of common stock (in dollars per share)	$ 0.1675	$ 0.1625	$ 0.5025	$ 0.48750