Quarterly Results for 2012 and 2011 (UNAUDITED) (Details) (USD $)	3 Months Ended										12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accrual for Environmental Loss Contingencies, Increase (Decrease) for Revision in Estimates											$ 797,000	$ 6,873,000	$ 3,201,000
Selected Quarterly Financial Information [Abstract]
Sales	434,306,000	408,988,000	371,926,000	355,780,000	388,423,000		385,091,000		357,397,000	357,731,000	1,571,000,000	1,488,642,000	1,315,233,000
Operating Income (Loss)	115,678,000	113,174,000	98,590,000	84,009,000	81,325,000	[1]	108,310,000		79,073,000	87,578,000	411,451,000	356,286,000	281,951,000
Net income	75,609,000	80,560,000	69,079,000	53,437,000	56,230,000	[1]	104,909,000	[2]	56,454,000	58,412,000	278,685,000	276,005,000	217,586,000
Basic EPS	$ 0.61	$ 0.66	$ 0.56	$ 0.44	$ 0.46		$ 0.86		$ 0.46	$ 0.48	$ 2.27	$ 2.27	$ 1.81
Diluted EPS	$ 0.59	$ 0.62	$ 0.54	$ 0.42	$ 0.45		$ 0.84		$ 0.45	$ 0.47	$ 2.17	$ 2.20	$ 1.79
Taxability of the alternative fuel mixture credit
Tax Adjustments, Settlements, and Unusual Provisions							16,000,000
Port Angeles Increase in Disposition Reserve [Member]
Accrual for Environmental Loss Contingencies, Increase (Decrease) for Revision in Estimates												6,500,000
Effect of Increase (Decrease) in Reserve for Revision in Estimates, Net of Tax												$ 4,100,000

[1] Fourth quarter 2011 included a pre-tax expense of $6.5 million ($4.1 million after tax) due to an increase in a disposition reserve.

[2] Third quarter 2011 included a benefit of $16.0 million from the reversal of a reserve related to the taxability of the AFMC.