Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash Flows from Operating Activities:
Net income	$ 76,785	$ 57,224
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	79,934	77,728
Amortization of financing costs	250	344
Amortization of net gain on treasury lock	(923)	(923)
Share-based compensation expense	4,704	3,788
Deferred income tax provision	(1,603)	(3,639)
Loss on disposals of property, plant and equipment	5,415	3,837
(Increase) decrease in assets -
Accounts receivable	(34,361)	(65,760)
Alternative fuel mixture tax credits receivable		31,770
Inventories	15,535	5,529
Prepaid expenses and other current assets	(12,845)	(16,964)
Increase (decrease) in liabilities -
Accounts payable	36,401	39,022
Accrued liabilities	(9,510)	(32,306)
Other, net	5,401	8,934
Net cash provided by operating activities	165,183	108,584
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(145,150)	(155,349)
Acquisition of business	(26,942)
Additions to other long term assets	(6,530)	(1,711)
Proceeds from disposals of property, plant and equipment	419	93
Net cash used for investing activities	(178,203)	(156,967)
Cash Flows from Financing Activities:
Payments on long-term debt	(330)	(307)
Settlement of treasury lock	9,910
Common stock dividends paid	(35,795)	(30,911)
Repurchases of common stock	(45,392)	(3,111)
Proceeds from exercise of stock options	6,335	2,761
Excess tax benefits from share-based awards	917	735
Net cash used for financing activities	(64,355)	(30,833)
Net decrease in cash and cash equivalents	(77,375)	(79,216)
Cash and cash equivalents, beginning of period	196,556	260,727
Cash and cash equivalents, end of period	$ 119,181	$ 181,511