Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 53,948	$ 34,599	$ 46,107	$ 83,903
Receivables, net	722,945	727,030
Inventories	287,309	226,583
Prepayments and other current assets	119,500	81,304
Current assets held for sale	430	479
Total current assets	1,184,132	1,069,995
Investments	138,620	137,613
Property, plant and equipment (Note 1)	7,397,321	6,770,829
Less accumulated depreciation, depletion and amortization	2,818,644	2,691,641	2,578,902
Net property, plant and equipment	4,578,677	4,079,188	3,931,327
Deferred charges and other assets:
Goodwill (Note 5)	664,922	631,791	631,791
Other intangible assets, net (Note 5)	10,815	3,837
Other	408,857	407,850
Noncurrent assets held for sale	2,087	4,392
Total deferred charges and other assets	1,086,681	1,047,870
Total assets	6,988,110	6,334,666	$ 6,284,467
Current liabilities:
Long-term debt due within one year	251,854	148,499
Accounts payable	358,505	312,327
Taxes payable	41,929	42,537
Dividends payable	39,695	38,573
Accrued compensation	69,007	72,919
Other accrued liabilities	221,059	186,010
Current liabilities held for sale	4,001	11,993
Total current liabilities	986,050	812,858
Long-term debt (Note 8)	1,856,841	1,566,354
Deferred credits and other liabilities:
Deferred income taxes	430,085	347,271
Other	1,148,359	1,179,140
Total deferred credits and other liabilities	1,578,444	1,526,411
Commitments and contingencies (Notes 16, 18 and 19)
Stockholders' equity:
Authorized - 500,000,000 shares, $1.00 par value Issued - 196,564,907 shares in 2018 and 195,843,297 shares in 2017	196,565	195,843
Other paid-in capital	1,248,576	1,233,412
Retained earnings	1,163,602	1,040,748
Accumulated other comprehensive loss	(38,342)	(37,334)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)
Total stockholders' equity	2,566,775	2,429,043
Total liabilities and stockholders' equity	$ 6,988,110	$ 6,334,666