Condensed Consolidated Statements 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	$ 125,078	$ 62,998
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	85,742	85,082
Amortization of financing costs	410	396
Amortization of net loss on treasury lock	2,827	2,572
Share-based compensation expense	6,774	5,731
Deferred income tax provision	(8,999)	159,157
Alternative fuel mixture credits	72,437	(87,897)
Loss on disposals of property, plant and equipment	3,455	3,672
Pension and postretirement benefits	28,023	6,905
Other, net	(961)	(14)
(Increase) decrease in assets -
Accounts receivable	(51,225)	(26,380)
Inventories	5,759	(2,065)
Prepaid expenses and other current assets	(15,695)	(15,184)
Increase (decrease) in liabilities -
Accounts payable	47,400	(23,845)
Accrued liabilities	(17,988)	(21,083)
Net cash provided by operating activities	283,037	150,045
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(80,891)	(69,322)
Acquisition of business		(35,393)
Treasury grant proceeds		57,399
Additions to other long term assets	(2,196)	(1,601)
Proceeds from disposals of property, plant and equipment	234	20
Net cash used for investing activities	(82,853)	(48,897)
Cash Flows from Financing Activities:
Proceeds on long-term debt		397,044
Payments on long-term debt	(7,974)	(7,929)
Financing costs paid		(892)
Settlement of treasury lock		(65,500)
Common stock dividends paid	(30,658)	(44,296)
Repurchases of common stock	(5,149)	(33,305)
Proceeds from exercise of stock options	2,125	11,184
Excess tax benefits from share-based awards	5,444	1,354
Other	(1,308)
Net cash (used for) provided by financing activities	(37,520)	257,660
Net increase in cash and cash equivalents	162,664	358,808
Cash and cash equivalents, beginning of period	207,393	156,313
Cash and cash equivalents, end of period	$ 370,057	$ 515,121