CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and equivalents	$ 938,615	$ 964,988
Accounts receivable, less allowance for doubtful accounts of $1,605 in 2018 and 2017	212,639	243,472
Inventories, at lower of cost or market	94,157	105,127
Prepaid expenses	39,936	35,087
Assets held for sale	22,696	22,929
Total current assets	1,308,043	1,371,603
Property, plant and equipment, at cost less accumulated depreciation, depletion and amortization of $12,422,869 in 2018 and $12,280,741 in 2017	8,207,736	8,220,031
Deferred income taxes	368,878	211,543
Deferred charges and other assets	53,553	57,765
Total assets	9,938,210	9,860,942
Current liabilities
Current maturities of long-term debt	9,557	9,902
Accounts payable	615,963	595,916
Income taxes payable	77,488	44,604
Other taxes payable	19,745	23,574
Other accrued liabilities	140,158	156,681
Liabilities associated with assets held for sale	3,160	3,530
Total current liabilities	866,071	834,207
Long-term debt, including capital lease obligation	2,898,850	2,906,520
Deferred income taxes	128,719	159,098
Asset retirement obligations	691,170	709,299
Deferred credits and other liabilities	661,093	631,627
Stockholders' equity
Cumulative Preferred Stock, par $100, authorized 400,000 shares, none issued
Common Stock, par $1.00, authorized 450,000,000 shares, issued 195,065,341 shares in 2018 and 195,055,724 in 2017	195,065	195,056
Capital in excess of par value	891,191	917,665
Retained earnings	5,400,474	5,245,242
Accumulated other comprehensive loss	(544,737)	(462,243)
Treasury stock	(1,249,686)	(1,275,529)
Total stockholders' equity	4,692,307	4,620,191
Total liabilities and stockholders' equity	$ 9,938,210	$ 9,860,942

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.