CONDENSED CONSOLIDATED STATEMENTS OF INCOME Unaudited - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Operating revenue	$ 172,632	$ 171,132	$ 304,879	$ 293,168
Operations:
Water production costs	65,373	64,131	112,979	106,199
Administrative and general	24,383	21,413	50,702	44,159
Other operations	20,724	18,328	38,364	34,452
Maintenance	5,389	4,708	10,828	10,820
Depreciation and amortization	20,953	19,218	41,668	38,419
Income taxes	4,347	10,606	4,118	9,722
Property and other taxes	6,407	6,057	13,111	12,173
Total operating (income) expenses	147,576	144,461	271,770	255,944
Net operating income	25,056	26,671	33,109	37,224
Other income and expenses:
Non-regulated revenue	4,845	3,739	9,264	7,201
Non-regulated expenses	(6,115)	(1,614)	(11,552)	(3,668)
Other components of net periodic benefit cost	(2,463)	(2,383)	(5,009)	(4,886)
Allowance for equity funds used during construction	710	879	1,621	1,658
Income tax benefit (expense) on other income and expenses	819	(246)	1,577	(1,135)
Net other (loss) income	(2,204)	375	(4,099)	(830)
Interest expense:
Interest expense	10,134	9,079	19,332	17,789
Allowance for borrowed funds used during construction	(304)	(564)	(799)	(1,058)
Net interest expense	9,830	8,515	18,533	16,731
Net income	$ 13,022	$ 18,531	$ 10,477	$ 19,663
Earnings per share:
Basic (in dollars per share)	$ 0.27	$ 0.39	$ 0.22	$ 0.41
Diluted (in dollars per share)	$ 0.27	$ 0.39	$ 0.22	$ 0.41
Weighted average shares outstanding:
Basic (in shares)	48,073	48,020	48,051	48,002
Diluted (in shares)	48,073	48,020	48,051	48,002
Dividends declared per share of common stock (in dollars per share)	$ 0.1875	$ 0.18	$ 0.3750	$ 0.3600