Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Current assets:
Cash and cash equivalents	$ 12,225	$ 20,776	$ 30,947
Restricted cash	3,494	3,369	2,958
Accounts receivable, net	282,602	269,153	257,772
Materials, supplies and fuel	87,676	117,299	82,045
Derivative assets, current	932	1,500	295
Income tax receivable, net	15,309	12,978	13,900
Regulatory assets, current	54,303	48,776	54,492
Other current assets	28,029	29,982	24,972
Current assets held for sale	0	0	24,724
Total current assets	484,570	503,833	492,105
Investments	41,247	41,013	40,927
Property, plant and equipment	6,127,050	6,000,015	5,608,539
Less: accumulated depreciation and depletion	(1,187,112)	(1,145,136)	(1,048,933)
Total property, plant and equipment, net	4,939,938	4,854,879	4,559,606
Other assets:
Goodwill	1,299,454	1,299,454	1,299,454
Intangible assets, net	14,136	14,337	7,357
Regulatory assets, non-current	232,404	235,459	212,740
Other assets, non-current	25,823	14,352	14,800
Total other assets, non-current	1,571,817	1,563,602	1,534,351
TOTAL ASSETS	7,037,572	6,963,327	6,626,989
Current liabilities:
Accounts payable	178,678	210,609	106,281
Accrued liabilities	196,072	215,501	194,040
Derivative liabilities, current	95	947	891
Regulatory liabilities, current	45,777	29,810	42,499
Notes payable	164,650	185,620	164,200
Current maturities of long-term debt	5,743	5,743	255,743
Current liabilities held for sale	0	0	24,910
Total current liabilities	591,015	648,230	788,564
Long-term debt	2,950,299	2,950,835	2,858,787
Deferred credits and other liabilities:
Deferred income tax liabilities, net	337,184	311,331	290,491
Regulatory liabilities, non-current	511,482	510,984	495,362
Benefit plan liabilities	145,883	145,147	160,580
Other deferred credits and other liabilities	118,007	109,377	105,221
Total deferred credits and other liabilities	1,112,556	1,076,839	1,051,654
Commitments and contingencies (See Notes 8, 10, 15, 16)
Equity:
Common stock $1 par value; 100,000,000 shares authorized; issued 60,378,020; 60,048,567; and 53,648,817 shares, respectively	60,378	60,049	53,649
Additional paid-in capital	1,469,410	1,450,569	1,151,933
Retained earnings	777,262	700,396	656,161
Treasury stock, at cost – 23,756; 44,253; and 53,959 shares, respectively	(1,432)	(2,510)	(3,049)
Accumulated other comprehensive income (loss)	(26,459)	(26,916)	(39,924)
Total stockholders’ equity	2,279,159	2,181,588	1,818,770
Noncontrolling interest	104,543	105,835	109,214
Total equity	2,383,702	2,287,423	1,927,984
TOTAL LIABILITIES AND TOTAL EQUITY	$ 7,037,572	$ 6,963,327	$ 6,626,989