Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Current assets:
Cash and cash equivalents	$ 57,241	$ 59,547	$ 66,070
Receivables, net	979,862	873,986	1,009,433
Inventories	312,285	291,167	286,223
Current regulatory assets	133,135	68,527	79,125
Prepayments and other current assets	83,364	44,120	61,706
Total current assets	1,565,887	1,337,347	1,502,557
Noncurrent assets:
Property, plant and equipment	8,634,737	8,300,770	8,203,751
Less accumulated depreciation, depletion and amortization	3,175,756	3,133,831	3,115,805
Net property, plant and equipment	5,458,981	5,166,939	5,087,946
Goodwill	717,646	714,963	712,677
Other intangible assets, net	22,241	25,496	26,376
Regulatory assets	379,245	379,381	369,764
Investments	171,859	165,022	158,440
Operating lease right-of-use assets	109,439	120,113	120,534
Other	143,565	144,111	147,205
Total noncurrent assets	7,002,976	6,716,025	6,622,942
Total assets	8,568,863	8,053,372	8,125,499
Current liabilities:
Short-term borrowings	50,000	50,000	75,000
Long-term debt due within one year	1,548	1,555	1,558
Accounts payable	525,704	426,264	436,718
Taxes payable	87,455	88,844	96,708
Dividends payable	43,212	42,611	41,608
Accrued compensation	105,867	90,629	110,730
Operating lease liabilities due within one year	30,502	33,655	33,770
Regulatory liabilities due within one year	16,491	31,450	39,837
Other accrued liabilities	212,140	198,514	231,061
Total current liabilities	1,072,919	963,522	1,066,990
Noncurrent liabilities:
Long-term debt	2,326,718	2,211,575	2,268,732
Deferred income taxes	557,582	516,098	533,524
Asset retirement obligations	455,522	440,356	425,567
Regulatory liabilities	426,141	428,075	434,936
Operating lease liabilities	79,397	86,868	87,140
Other	318,306	327,773	295,845
Total noncurrent liabilities	4,163,666	4,010,745	4,045,744
Commitments and contingencies
Stockholders' equity:
Common stock	203,889	201,061	201,061
Other paid-in capital	1,458,208	1,371,385	1,366,494
Retained earnings	1,720,232	1,558,363	1,489,085
Accumulated other comprehensive loss	(46,425)	(48,078)	(40,249)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total stockholders' equity	3,332,278	3,079,105	3,012,765
Total liabilities and stockholders' equity	$ 8,568,863	$ 8,053,372	$ 8,125,499
Common Stock, Shares Authorized	500,000,000	500,000,000	500,000,000
Common Stock, Par or Stated Value Per Share	$ 1.00	$ 1.00	$ 1.00
Common Stock, Shares, Issued	203,889,661	201,061,198	201,061,198
Treasury Stock, Common, Shares	538,921	538,921	538,921