CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 201,827	$ 90,864
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	469,022	335,421
Deferred income tax expense	107,235	42,714
(Gain) / loss on sale of assets	(4,601)	(67,042)
Exploration expense	807	12,118
Unrealized (gain) / loss on derivative instruments		449
Amortization of debt issuance costs	2,767	4,300
Stock-based compensation, pension and other	36,684	37,518
Changes in assets and liabilities:
Accounts receivable, net	(6,321)	10,747
Inventories	(6,665)	3,582
Other current assets	(1,547)	(1,125)
Accounts payable and accrued liabilities	(19,837)	(16,391)
Income taxes	(3,639)	205
Other assets and liabilities	228	1,752
Stock-based compensation tax benefit	(9,284)
Net cash provided by operating activities	766,676	455,112
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(843,528)	(669,198)
Proceeds from sale of assets	15,174	132,740
Investment in equity method investment	(8,624)	(4,488)
Net cash used in investing activities	(836,978)	(540,946)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings from debt	585,000	280,000
Repayments of debt	(510,000)	(168,000)
Stock-based compensation tax benefit	9,284
Dividends paid	(16,830)	(12,561)
Capitalized debt issuance costs		(5,005)
Other	44	(1,010)
Net cash provided by financing activities	67,498	93,424
Net (decrease) / increase in cash and cash equivalents	(2,804)	7,590
Cash and cash equivalents, beginning of period	30,736	29,911
Cash and cash equivalents, end of period	$ 27,932	$ 37,501