Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Current assets:
Cash and cash equivalents	$ 58,764	$ 34,599	$ 50,735
Receivables, net	664,319	727,030	554,185
Inventories	257,792	226,583	250,609
Prepayments and other current assets	59,481	81,304	79,254
Current assets held for sale	458	479	7,290
Total current assets	1,040,814	1,069,995	942,073
Investments	138,451	137,613	129,009
Property, plant and equipment	6,842,967	6,770,829	6,544,077
Less accumulated depreciation, depletion and amortization	2,725,484	2,691,641	2,609,303
Net property, plant and equipment	4,117,483	4,079,188	3,934,774
Deferred charges and other assets:
Goodwill	631,791	631,791	631,791
Other intangible assets, net	3,465	3,837	5,347
Other	412,456	407,850	409,745
Noncurrent assets held for sale	4,392	4,392	95,719
Total deferred charges and other assets	1,052,104	1,047,870	1,142,602
Total assets	6,348,852	6,334,666	6,148,458
Current liabilities:
Long-term debt due within one year	149,199	148,499	43,499
Accounts payable	267,994	312,327	239,013
Taxes payable	57,354	42,537	74,638
Dividends payable	38,573	38,573	37,767
Accrued compensation	35,087	72,919	32,350
Other accrued liabilities	204,328	186,010	188,373
Current liabilities held for sale	11,726	11,993	2,394
Total current liabilities	764,261	812,858	618,034
Long-term debt	1,630,343	1,566,354	1,659,507
Deferred credits and other liabilities:
Deferred income taxes	346,218	347,271	666,905
Other	1,181,919	1,179,140	890,107
Total deferred credits and other liabilities	1,528,137	1,526,411	1,557,012
Commitments and contingencies
Stockholders' equity:
Preferred stocks	0	0	15,000
Common stockholders' equity:
Authorized - 500,000,000 shares, $1.00 par value Shares issued - 195,843,297 at March 31, 2018 and 2017 and December 31, 2017	195,843	195,843	195,843
Other paid-in capital	1,227,285	1,233,412	1,231,171
Retained earnings	1,051,469	1,040,748	911,702
Accumulated other comprehensive loss	(44,860)	(37,334)	(36,185)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)	(3,626)
Total common stockholders' equity	2,426,111	2,429,043	2,298,905
Total stockholders' equity	2,426,111	2,429,043	2,313,905
Total liabilities and stockholders' equity	$ 6,348,852	$ 6,334,666	$ 6,148,458