Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 268,037	$ 207,393
Accounts receivable, net of allowance for doubtful accounts and customer deductions of $5,827 and $5,353 as of March 31, 2013 and December 31, 2012, respectively	391,683	352,142
Inventories	270,181	268,767
Prepaid expenses and other current assets	24,279	20,915
Federal and state income taxes receivable	36,132	65,488
Deferred income taxes	21,324	22,328
Total current assets	1,011,636	937,033
Property, plant and equipment, net	1,353,202	1,366,069
Goodwill	67,160	67,160
Other intangible assets, net	37,436	38,283
Other long-term assets	46,504	45,223
Total assets	2,515,938	2,453,768
Current liabilities:
Current maturities of long-term debt	15,000	15,000
Capital lease obligations	980	964
Accounts payable	142,856	117,510
Dividends payable	30,669
Accrued interest	5,157	3,676
Accrued liabilities	91,718	122,696
Total current liabilities	286,380	259,846
Long-term liabilities:
Long-term debt	774,890	778,630
Capital lease obligations	24,653	24,904
Deferred income taxes	123,782	125,109
Pension and postretirement benefit plans	171,163	164,538
Cellulosic biofuel tax reserve	102,051	102,051
Other long-term liabilities	31,200	29,229
Total long-term liabilities	1,227,739	1,224,461
Stockholders' equity:
Common stock, par value $0.01 per share, 300,000,000 shares authorized, 98,093,425 and 98,142,782 shares issued as of March 31, 2013 and December 31, 2012, respectively	981	981
Additional paid in capital	382,395	378,794
Retained earnings	729,727	703,728
Accumulated other comprehensive loss, net of tax:
Unfunded employee benefit obligations	(80,110)	(81,999)
Total accumulated other comprehensive loss	(111,284)	(114,042)
Total stockholders' equity	1,001,819	969,461
Total liabilities and stockholders' equity	2,515,938	2,453,768
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Treasury Lock
Accumulated other comprehensive loss, net of tax:
Unrealized loss	(30,787)	(31,651)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Foreign Exchange Contract
Accumulated other comprehensive loss, net of tax:
Unrealized loss	$ (387)	$ (392)