CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 131,938	$ 54,255
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	300,042	224,973
Deferred income tax expense	69,662	27,073
(Gain) / loss on sale of assets	(180)	(67,168)
Exploration expense	806	10,925
Unrealized (gain) / loss on derivative instruments		300
Amortization of debt issuance costs	1,842	3,334
Stock-based compensation, pension and other	27,355	26,987
Changes in assets and liabilities:
Accounts receivable, net	(32,551)	25,214
Inventories	(4,103)	9,293
Other current assets	(2,733)	(3,691)
Accounts payable and accrued liabilities	9,661	(28,675)
Income taxes	(4,971)	4,775
Other assets and liabilities	547	3,547
Stock-based compensation tax benefit	(7,348)
Net cash provided by operating activities	489,967	291,142
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(524,056)	(411,327)
Proceeds from sale of assets	906	132,715
Investment in equity method investment	(4,250)	(2,088)
Net cash used in investing activities	(527,400)	(280,700)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings from debt	325,000	170,000
Repayments of debt	(270,000)	(148,000)
Stock-based compensation tax benefit	7,348
Dividends paid	(8,407)	(8,368)
Capitalized debt issuance costs		(5,005)
Other	33	(339)
Net cash provided by financing activities	53,974	8,288
Net (decrease) / increase in cash and cash equivalents	16,541	18,730
Cash and cash equivalents, beginning of period	30,736	29,911
Cash and cash equivalents, end of period	$ 47,277	$ 48,641