Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Current assets:
Cash and cash equivalents	$ 55,094	$ 59,547	$ 116,526
Receivables, net	784,582	873,986	835,468
Inventories	316,737	291,167	305,958
Current regulatory assets	98,452	68,527	55,206
Prepayments and other current assets	68,409	44,120	60,230
Total current assets	1,323,274	1,337,347	1,373,388
Noncurrent assets:
Property, plant and equipment	8,288,879	8,300,770	8,008,338
Less accumulated depreciation, depletion and amortization	3,096,371	3,133,831	3,039,812
Net property, plant and equipment	5,192,508	5,166,939	4,968,526
Goodwill	714,963	714,963	713,527
Other intangible assets, net	23,961	25,496	34,250
Regulatory assets	379,917	379,381	348,189
Investments	167,741	165,022	145,237
Operating lease right-of-use assets	116,663	120,113	114,382
Other	150,248	144,111	153,017
Total noncurrent assets	6,746,001	6,716,025	6,477,128
Total assets	8,069,275	8,053,372	7,850,516
Current liabilities:
Short-term borrowings	50,000	50,000	0
Long-term debt due within one year	1,552	1,555	16,560
Accounts payable	379,348	426,264	384,339
Taxes payable	88,711	88,844	58,743
Dividends payable	42,740	42,611	41,608
Accrued compensation	69,612	90,629	55,199
Regulatory liabilities due within one year	34,266	31,450	60,072
Operating lease liabilities due within one year	32,562	33,655	31,141
Other accrued liabilities	201,246	198,514	176,817
Total current liabilities	900,037	963,522	824,479
Noncurrent liabilities:
Long-term debt	2,251,722	2,211,575	2,438,675
Deferred income taxes	528,551	516,098	515,711
Regulatory liabilities	429,060	428,075	443,205
Asset retirement obligations	445,170	440,356	417,469
Operating lease liabilities	84,494	86,868	83,414
Other	329,935	327,773	290,971
Total noncurrent liabilities	4,068,932	4,010,745	4,189,445
Commitments and contingencies
Stockholders' equity:
Common stock	201,733	201,061	201,061
Other paid-in capital	1,382,158	1,371,385	1,360,564
Retained earnings	1,567,551	1,558,363	1,319,988
Accumulated other comprehensive loss	(47,510)	(48,078)	(41,395)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total stockholders' equity	3,100,306	3,079,105	2,836,592
Total liabilities and stockholders' equity	$ 8,069,275	$ 8,053,372	$ 7,850,516
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	201,733,458	201,061,198	201,061,198
Treasury Stock, Common, Shares	538,921	538,921	538,921