CONDENSED CONSOLIDATED STATEMENTS OF INCOME Unaudited - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Operating revenue	$ 184,268	$ 183,543	$ 458,440	$ 449,942
Operations:
Water production costs	70,175	60,437	168,833	158,661
Administrative and general	23,844	30,737	75,037	85,069
Other operations	19,561	17,872	57,766	51,227
Maintenance	5,545	5,952	17,542	15,735
Depreciation and amortization	15,884	15,342	47,772	46,015
Income taxes	13,247	15,293	19,192	21,008
Property and other taxes	5,957	5,709	17,439	16,036
Total operating (income) expense	154,213	151,342	403,581	393,751
Net operating income (loss)	30,055	32,201	54,859	56,191
Other income and expenses:
Non-regulated revenue	3,397	3,814	10,589	10,540
Non-regulated expenses	(2,517)	(4,454)	(8,306)	(10,201)
Income tax (expense) benefit on other income and expenses	(349)	262	(914)	(131)
Net other income (loss)	531	(378)	1,369	208
Interest expense:
Interest expense	8,485	7,201	24,984	21,331
Less: capitalized interest	(774)	(498)	(2,341)	(1,472)
Net interest expense	7,711	6,703	22,643	19,859
Net income	$ 22,875	$ 25,120	$ 33,585	$ 36,540
Earnings per share:
Basic (in dollars per share)	$ 0.48	$ 0.52	$ 0.70	$ 0.76
Diluted (in dollars per share)	$ 0.48	$ 0.52	$ 0.70	$ 0.76
Weighted average shares outstanding:
Basic (in shares)	47,969	47,878	47,949	47,861
Diluted (in shares)	47,969	47,887	47,952	47,877
Dividends declared per share of common stock (in dollars per share)	$ 0.1725	$ 0.1675	$ 0.5175	$ 0.5025