CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 42,824	$ 18,318
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation, depletion and amortization	148,653	110,357
Deferred income tax expense	23,574	9,724
(Gain) / loss on sale of assets	96	535
Exploration expense	666	49
Unrealized (gain) / loss on derivative instruments		(42)
Amortization of debt issuance costs	897	1,064
Stock-based compensation, pension and other	17,655	(1,470)
Changes in assets and liabilities:
Accounts receivable, net	(243)	19,261
Inventories	2,896	9,048
Other current assets	983	518
Accounts payable and accrued liabilities	(27,885)	(38,149)
Income taxes	4,349	2,187
Other assets and liabilities	358	380
Stock-based compensation tax benefit	(2,138)
Net cash provided by operating activities	212,685	131,780
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(260,169)	(188,547)
Proceeds from sale of assets	486	1,280
Investment in equity method investment	(1,250)
Net cash used in investing activities	(260,933)	(187,267)
CASH FLOWS FROM FINANCING ACTIVITIES
Borrowings from debt	135,000	90,000
Repayments of debt	(95,000)	(28,000)
Stock-based compensation tax benefit	2,138
Dividends paid	(4,201)	(4,177)
Other	32	81
Net cash provided by financing activities	37,969	57,904
Net (decrease) / increase in cash and cash equivalents	(10,279)	2,417
Cash and cash equivalents, beginning of period	30,736	29,911
Cash and cash equivalents, end of period	$ 20,457	$ 32,328