CONDENSED CONSOLIDATED STATEMENTS OF (LOSS) INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Operating revenue	$ 175,484		$ 179,031		$ 301,047	$ 305,142
Operations:
Water production costs	71,142		64,635		125,118	110,227
Administrative and general	26,939		25,434		56,619	54,531
Other operations	25,898		22,542		39,872	40,363
Maintenance	6,722		5,692		13,795	12,147
Depreciation and amortization	24,542		22,326		49,034	44,694
Income taxes	622		4,321		(3,315)	1,330
Property and other taxes	7,126		7,068		14,354	14,361
Total operating (income) expenses	162,991		152,018		295,477	277,653
Net operating income	12,493		27,013		5,570	27,489
Other income and expenses:
Non-regulated revenue	4,208		5,130		8,035	10,031
Non-regulated expenses	(492)		(3,900)		(8,946)	(6,119)
Other components of net periodic benefit cost	(1,332)		(1,192)		(2,762)	(2,451)
Allowance for equity funds used during construction	1,705		1,686		3,319	3,219
Income tax expense on other income and expenses	(820)		(487)		93	(1,315)
Net other income	3,269		1,237		(261)	3,365
Interest expense:
Interest expense	11,613		12,178		22,411	23,253
Allowance for borrowed funds used during construction	(1,132)		(924)		(2,076)	(1,755)
Net interest expense	10,481		11,254		20,335	21,498
Net income	$ 5,281	$ (20,307)	$ 16,996	$ (7,640)	$ (15,026)	$ 9,356
Earnings per share:
Basic (in dollars per share)	$ 0.11		$ 0.35		$ (0.31)	$ 0.19
Diluted (in dollars per share)	$ 0.11		$ 0.35		$ (0.31)	$ 0.19
Weighted average shares outstanding:
Basic (in shares)	48,936		48,136		48,759	48,111
Diluted (in shares)	48,936		48,136		48,759	48,111