CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Current assets
Cash and equivalents		$ 1,058,487	$ 872,797
Canadian government securities with maturities greater than 90 days at the date of acquisition		40,104	111,542
Accounts receivable, less allowance for doubtful accounts of $1,605 in 2017 and 2016		232,558	357,099
Inventories, at lower of cost or market		131,952	127,071
Prepaid expenses		55,237	63,604
Assets held for sale		22,245	27,070
Total current assets		1,540,583	1,559,183
Property, plant and equipment, at cost less accumulated depreciation, depletion and amortization of $11,795,083 in 2017 and $12,607,815 in 2016		8,164,116	8,316,188
Deferred charges and other assets		432,102	420,489
Total assets		10,136,801	10,295,860
Current liabilities
Current maturities of long-term debt		559,216	569,817
Accounts payable		595,775	784,975
Income taxes payable		56,304	13,920
Other taxes payable		38,284	28,167
Other accrued liabilities		105,111	102,777
Liabilities associated with assets held for sale		2,952	2,776
Total current liabilities		1,357,642	1,502,432
Long-term debt, including capital lease obligation		2,367,059	2,422,750
Deferred income taxes		107,573	69,081
Asset retirement obligations		703,364	681,528
Deferred credits and other liabilities		623,475	617,490
Liabilities associated with assets held for sale			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		903,542	916,799
Retained earnings		5,684,211	5,729,596
Accumulated other comprehensive loss	[1]	(529,592)	(628,212)
Treasury stock		(1,275,529)	(1,296,560)
Total stockholders' equity		4,977,688	4,916,679
Total liabilities and stockholders' equity		$ 10,136,801	$ 10,295,860

[1] All amounts are presented net of income taxes.