Debt (Details Textual 1) (USD $)	1 Months Ended	6 Months Ended	12 Months Ended			3 Months Ended				3 Months Ended				6 Months Ended																							1 Months Ended			12 Months Ended							1 Months Ended				12 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2011	Nov. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 6.30% notes due 2013 [Member]	Dec. 31, 2011 6.30% notes due 2013 [Member]	Dec. 31, 2010 6.30% notes due 2013 [Member]	Jun. 30, 2008 6.30% notes due 2013 [Member]	Jun. 30, 2011 5.60% notes due 2012 [Member]	Dec. 31, 2011 5.60% notes due 2012 [Member]	Dec. 31, 2010 5.60% notes due 2012 [Member]	Dec. 31, 2007 5.60% notes due 2012 [Member]	Jun. 30, 2011 5.60% notes due 2012 [Member] 6.30% notes due 2013 [Member]	Dec. 31, 2011 10.125% notes due 2015 [Member]	Dec. 31, 2010 10.125% notes due 2015 [Member]	Feb. 28, 2009 10.125% notes due 2015 [Member]	Dec. 31, 2011 6.50% notes due 2016 [Member]	Jun. 30, 2011 6.50% notes due 2016 [Member]	Dec. 31, 2010 6.50% notes due 2016 [Member]	Dec. 31, 2011 6.40% notes due 2017 [Member]	Dec. 31, 2010 6.40% notes due 2017 [Member]	Dec. 31, 2007 6.40% notes due 2017 [Member]	Dec. 31, 2011 7.00% notes due 2018 [Member]	Dec. 31, 2010 7.00% notes due 2018 [Member]	Jun. 30, 2008 7.00% notes due 2018 [Member]	Dec. 31, 2011 10.375% notes due 2018 [Member]	Dec. 31, 2010 10.375% notes due 2018 [Member]	Feb. 28, 2009 10.375% notes due 2018 [Member]	Dec. 31, 2011 7.50% notes due 2021 [Member]	Jun. 30, 2011 7.50% notes due 2021 [Member]	Dec. 31, 2011 7.15% notes due 2037 [Member]	Dec. 31, 2010 7.15% notes due 2037 [Member]	Dec. 31, 2007 7.15% notes due 2037 [Member]	Dec. 31, 2010 Floating-rate notes due 2010 [Member]	Dec. 31, 2007 Floating-rate notes due 2010 [Member]	Jul. 31, 2010 Floating-rate term loan due in 2011 [Member]	Jan. 31, 2010 Floating-rate term loan due in 2011 [Member]	Nov. 30, 2009 Floating-rate term loan due in 2011 [Member]	Dec. 31, 2011 Floating-rate term loan due in 2011 [Member] Quarter	Dec. 31, 2010 Floating-rate term loan due in 2011 [Member]	Aug. 31, 2010 Floating-rate term loan due in 2011 [Member]	Jun. 30, 2008 Floating-rate term loan due in 2011 [Member]	Dec. 31, 2011 Floating-rate term loan due 2015 [Member]	Dec. 31, 2010 Floating-rate term loan due 2015 [Member]	Jul. 07, 2010 Floating-rate term loan due 2015 [Member]	Aug. 31, 2010 Private placement notes [Member]	Sep. 30, 2010 Industrial revenue bonds [Member]	Dec. 31, 2011 Industrial revenue bonds [Member]	Dec. 31, 2010 Industrial revenue bonds [Member]	Dec. 31, 1991 Medium-term notes [Member]	Dec. 31, 2011 Medium-term notes [Member] Y	Dec. 31, 2010 Medium-term notes [Member]	Feb. 28, 2009 Long term notes issued [Member]	Jun. 30, 2008 Long term notes issued [Member]	Dec. 31, 2007 Long term notes issued [Member]	Nov. 30, 2007 Industrial revenue bonds maturing in 2012 [Member]	Nov. 30, 2007 Industrial revenue bonds maturing in 2021 [Member]	Nov. 30, 2007 Industrial revenue bonds maturing in 2022 [Member]	Dec. 31, 2011 Other notes [Member]	Dec. 31, 2010 Other notes [Member]
Debt (Textual)
Coupon rate of notes						6.30%	6.30%	6.30%	6.30%	5.60%	5.60%	5.60%	5.60%		10.125%	10.125%	10.125%	6.50%	6.50%		6.40%	6.40%	6.40%	7.00%	7.00%	7.00%	10.375%	10.375%	10.375%	7.50%	7.50%	7.15%	7.15%	7.15%
Decrease in unamortized discounts							$ 92,000	$ 271,000			$ 49,000	$ 227,000			$ 338,000	$ 403,000					$ 131,000	$ 148,000		$ 307,000	$ 342,000		$ 1,474,000	$ 1,609,000				$ 643,000	$ 676,000
Increase (decrease) in unamortized deferred gain realized															3,802,000			18,293,000
Effective interest rate							7.48%	7.48%			6.57%	6.57%			9.59%	9.59%		6.02%			7.41%	7.41%		7.87%	7.87%		10.62%	10.62%		7.75%		8.05%	8.05%
Purchase of long term notes						109,556,000				165,443,000
Amount of outstanding balance of loan repaid																																					100,000,000
Total consideration paid for debt														294,533,000
Premium paid for purchase of debt														19,534,000
Voluntary prepayment of debt																																						75,000,000	50,000,000		175,000,000						15,000,000	3,550,000
Amount of quarterly principal payments of loan																																									15,000,000
Frequency of periodic principal payments																																									quarterly
Number of quarters principal payments were made																																								5
Amount of final principal payment				5,000,000																															325,000,000							100,000,000
Date of final principal payment																																									August 2010
Fixed interest rate																																				5.25%
Long-term notes face amount	1,100,000,000	1,100,000,000							250,000,000				300,000,000	274,999,000			150,000,000		500,000,000				350,000,000			400,000,000			250,000,000		600,000,000			250,000,000		325,000,000							300,000,000			450,000,000					81,000,000			400,000,000	650,000,000	1,225,000,000
Maturity period of notes, minimum																																																			3 years
Maturity period of notes, maximum																																																			30 years
Coupon rate of notes, minimum																																																			7.59%
Coupon rate of notes, maximum																																																			8.85%
Amount of notes outstanding																																																				16,000,000
Weighted-average maturity (in years)																																																				4.3
Weighted-average interest rate																																																				8.76%
Industrial revenue bonds																																																									2,250,000	1,300,000	14,000,000
Long-term Debt			2,815,439,000		2,432,762,000		140,352,000	249,729,000			134,508,000	299,773,000			153,464,000	149,597,000		518,293,000		0	349,869,000	349,852,000		399,693,000	399,658,000		248,526,000	248,391,000				239,545,000	249,324,000											0	450,000,000				14,000,000	14,000,000		16,000,000	21,000,000							1,189,000	1,438,000
Outstanding amount under revolving credit facility repaid	275,000,000
Recognition of unamortized deferred financing costs		2,423,000
Expenses related to partial termination of debt	4,711,000
Combined expense			24,245,000
Industrial revenue bonds backed by a letter of credit			$ 14,000,000
Minimum fixed charge coverage ratio			90.00%
Maximum total debt as a percentage of total capital			65.00%
Total debt as a percentage of total capital			42.60%		40.70%