CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
OPERATING ACTIVITIES
Net income (loss)	$ (49,444)	$ 40,616
Adjustments to reconcile net income (loss) to net cash flows provided by (used in) operating activities:
Depreciation and depletion	81,190	66,493
Deferred income tax benefit	(61,941)	(10,894)
Amortization of debt issuance costs	9,982	3,644
Other	14,922	8,756
Decrease (increase) in current assets:
Receivables	(58,494)	16,889
Inventories	5,428	(63,192)
Prepaid expenses and other current assets	6,502	5,462
Increase (decrease) in current liabilities:
Accounts payable	22,534	37,604
Accrued expenses and other current liabilities	9,923	(34,524)
Cash flows provided by (used in) operating activities	(19,398)	70,854
INVESTING ACTIVITIES
Additions to property, plant and equipment	(34,027)	(120,845)
Proceeds from sales of investments		12,228
Other	1,021	(85)
Cash flows used in investing activities	(33,006)	(108,702)
FINANCING ACTIVITIES
Proceeds from issuance of debt	450,000
Borrowings under revolving credit agreement	320,778	135,294
Repayments on revolving credit agreement	(320,778)	(70,156)
Retirements of debt	(254,687)	(9,177)
Dividends paid	(7,816)	(7,806)
Debt issuance costs	(15,163)
Other	(328)	(624)
Cash flows provided by financing activities	172,006	47,531
Effect of foreign exchange rates on cash	(412)	87
Net increase in cash and cash equivalents	119,190	9,770
Cash and cash equivalents at beginning of period	116,601	128,430
Cash and cash equivalents at end of period	$ 235,791	$ 138,200