Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 66,459	$ 53,948	$ 34,599	$ 46,107
Receivables, net	836,605	722,945
Inventories	278,407	287,309
Prepayments and other current assets	115,805	119,500
Current assets held for sale	425	430
Total current assets	1,297,701	1,184,132
Investments	148,656	138,620
Property, plant and equipment	7,908,628	7,397,321
Less accumulated depreciation, depletion and amortization	2,991,486	2,818,644	2,691,641
Net property, plant and equipment	4,917,142	4,578,677	4,079,188
Deferred charges and other assets:
Goodwill	681,358	664,922	631,791
Other intangible assets, net	15,246	10,815
Operating lease right-of-use assets	115,323
Other	506,207	408,857
Noncurrent assets held for sale	1,426	2,087
Total deferred charges and other assets	1,319,560	1,086,681
Total assets	7,683,059	6,988,110	$ 6,334,666
Current liabilities:
Long-term debt due within one year	16,540	251,854
Accounts payable	403,391	358,505
Taxes payable	48,970	41,929
Dividends payable	41,580	39,695
Accrued compensation	99,269	69,007
Current operating lease liabilities	31,664
Other accrued liabilities	221,502	221,059
Current liabilities held for sale	3,511	4,001
Total current liabilities	866,427	986,050
Long-term debt	2,226,567	1,856,841
Deferred credits and other liabilities:
Deferred income taxes	506,583	430,085
Noncurrent operating lease liabilities	83,742
Other	1,152,494	1,148,359
Total deferred credits and other liabilities	1,742,819	1,578,444
Commitments and contingencies (Note 20)
Stockholders' equity:
Authorized - 500,000,000 shares, $1.00 par value Shares issued - 200,922,790 at December 31, 2019 and 196,564,907 at December 31, 2018	200,923	196,565
Other paid-in capital	1,355,404	1,248,576
Retained earnings	1,336,647	1,163,602
Accumulated other comprehensive loss	(42,102)	(38,342)
Treasury stock at cost - 538,921 shares	(3,626)	(3,626)
Total stockholders' equity	2,847,246	2,566,775
Total liabilities and stockholders' equity	$ 7,683,059	$ 6,988,110