CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and equivalents		$ 964,988	$ 872,797
Canadian government securities with maturities greater than 90 days at the date of acquisition			111,542
Accounts receivable, less allowance for doubtful accounts of $1,605 in 2017 and 2016		243,472	357,099
Inventories, at lower of cost or market		105,127	127,071
Prepaid expenses		35,087	63,604
Assets held for sale		22,929	27,070
Total current assets		1,371,603	1,559,183
Property, plant and equipment, at cost less accumulated depreciation, depletion and amortization of $12,280,741 in 2017 and $12,607,815 in 2016		8,220,031	8,316,188
Deferred income taxes		211,543	365,935
Deferred charges and other assets		57,765	54,554
Total assets		9,860,942	10,295,860
Current liabilities
Current maturities of long-term debt		9,902	569,817
Accounts payable		595,916	784,975
Income taxes payable		44,604	13,920
Other taxes payable		23,574	28,167
Other accrued liabilities		156,681	102,777
Liabilities associated with assets held for sale		3,530	2,776
Total current liabilities		834,207	1,502,432
Long-term debt, including capital lease obligation		2,906,520	2,422,750
Deferred income taxes		159,098	69,081
Asset retirement obligations		709,299	681,528
Deferred credits and other liabilities		631,627	617,490
Liabilities associated with assets held for sale	[1]		85,900
Stockholders' equity
Cumulative Preferred Stock, par $100, authorized 400,000 shares, none issued
Common Stock, par $1.00, authorized 450,000,000 shares, issued 195,055,724 shares in 2017 and 2016		195,056	195,056
Capital in excess of par value		917,665	916,799
Retained earnings		5,245,242	5,729,596
Accumulated other comprehensive loss		(462,243)	(628,212)
Treasury stock		(1,275,529)	(1,296,560)
Total stockholders' equity		4,620,191	4,916,679
Total liabilities and stockholders' equity		$ 9,860,942	$ 10,295,860

[1] Liabilities held for sale related to Seal properties in Canada which were sold in January 2017.