Long-Term Debt (Details) (USD $)	3 Months Ended			12 Months Ended											12 Months Ended				1 Months Ended		3 Months Ended	4 Months Ended	12 Months Ended		1 Months Ended		3 Months Ended		12 Months Ended		1 Months Ended			1 Months Ended			1 Months Ended		12 Months Ended
	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Revolving credit facility	Dec. 31, 2010 Revolving credit facility	Dec. 31, 2009 Revolving credit facility	Dec. 31, 2011 Revolving credit facility Minimum	Dec. 31, 2011 Revolving credit facility Maximum	Dec. 31, 2011 Revolving credit facility LIBOR Loans	Dec. 31, 2011 Revolving credit facility LIBOR Loans Maximum	Dec. 31, 2011 Revolving credit facility Alternate Base Rate Loans Maximum	Dec. 31, 2011 Revolving credit facility Prime rate	Dec. 31, 2011 Revolving credit facility Federal Funds rate	Dec. 31, 2011 Revolving credit facility One month LIBOR	Dec. 31, 2011 Senior Notes Y	May 31, 2009 2014 Senior Notes, 6.875% interest, issued October 2004 and May 2009 and due November 2014	Oct. 31, 2004 2014 Senior Notes, 6.875% interest, issued October 2004 and May 2009 and due November 2014	Dec. 31, 2010 2014 Senior Notes, 6.875% interest, issued October 2004 and May 2009 and due November 2014	Dec. 31, 2006 2016 Senior Notes, 8.5% interest, issued July 2006 and due July 2016	Dec. 31, 2011 2016 Senior Notes, 8.5% interest, issued July 2006 and due July 2016	Dec. 31, 2010 2016 Senior Notes, 8.5% interest, issued July 2006 and due July 2016	May 31, 2008 2018 Senior Notes, 8.75% interest, issued April and May 2008 and due April 2018	Apr. 30, 2008 2018 Senior Notes, 8.75% interest, issued April and May 2008 and due April 2018	Dec. 31, 2011 2018 Senior Notes, 8.75% interest, issued April and May 2008 and due April 2018	Mar. 31, 2011 2018 Senior Notes, 8.75% interest, issued April and May 2008 and due April 2018	Dec. 31, 2011 2018 Senior Notes, 8.75% interest, issued April and May 2008 and due April 2018	Dec. 31, 2010 2018 Senior Notes, 8.75% interest, issued April and May 2008 and due April 2018	Nov. 30, 2010 2020 Senior Notes, 6.75% interest, issued November 2010and due November 2020	Dec. 31, 2011 2020 Senior Notes, 6.75% interest, issued November 2010and due November 2020	Dec. 31, 2010 2020 Senior Notes, 6.75% interest, issued November 2010and due November 2020	Mar. 31, 2011 2021 Senior Notes, 6.5% interest, issued February and March 2011 and due August 2021	Feb. 28, 2011 2021 Senior Notes, 6.5% interest, issued February and March 2011 and due August 2021	Dec. 31, 2011 2021 Senior Notes, 6.5% interest, issued February and March 2011 and due August 2021	Nov. 30, 2011 2022 Senior Notes, 6.25% interest, issued October 2011 and due June 2022	Dec. 31, 2011 2022 Senior Notes, 6.25% interest, issued October 2011 and due June 2022	Dec. 31, 2011 2016 and 2018 Senior Notes	Dec. 31, 2011 Revolving Credit Facility LIBOR Loans Minimum	Dec. 31, 2011 Revolving Credit Facility Alternate Base Rate Loans Minimum
Long-Term Debt
Long-term debt, net of discounts	$ 1,846,062,000		$ 1,273,434,000	$ 1,846,062,000	$ 1,273,434,000		$ 66,000,000																	$ 274,358,000			$ 80,983,000		$ 80,983,000	$ 499,076,000		$ 500,000,000	$ 500,000,000			$ 499,079,000		$ 700,000,000
Debt instrument, stated interest rate percentage							4.00%												6.875%	6.875%			8.50%				8.75%		8.75%			6.75%				6.50%		6.25%
Long-term debt, discounts	1,050,000		1,566,000	1,050,000	1,566,000																		0	642,000			129,000		129,000	924,000						921,000
Credit facility current lending capacity							900,000,000
Uncommitted accordion feature							250,000,000
Deferred financing costs				20,163,000	20,912,000	8,554,000	2,100,000	11,200,000	4,400,000
Basis of variable interest rate												LIBOR			Prime Rate	Federal Funds Rate	One month LIBOR
Spread on variable rate basis (as a percent)													2.75%	1.75%		0.50%	1.00%																							1.75%	0.75%
Letters of credit maximum borrowing capacity							150,000,000
Short-term swingline loan maximum borrowing capacity							10,000,000
Principal amount due in 2016							66,000,000
Interest coverage ratio, numerator										2.75
Interest coverage ratio, denominator										1.0
Total leverage ratio, numerator											5.25
Total leverage ratio, denominator											1.0
Borrowings outstanding amount							66,000,000
Letters of credit outstanding amount	19,300,000			19,300,000
Credit facility remaining borrowing capacity							814,700,000
Outstanding senior notes																											81,100,000		81,100,000			500,000,000				500,000,000		700,000,000
Aggregate principal amount of debt issued																			150,000,000	225,000,000		275,000,000			100,000,000	400,000,000					500,000,000			200,000,000	300,000,000		700,000,000
Combined proceeds after including initial purchasers' premium and deducting the underwriting fees and the other expenses of the offering																									488,500,000						490,300,000			492,000,000			688,000,000
Debt redeemed																							275,000,000				253,300,000	165,600,000	419,000,000
Loss on redemption of debt	35,500,000	43,300,000	46,300,000	78,996,000	46,326,000																46,300,000																		79,000,000
Issue price as percentage of par value																																		99.50%
Write off of the unamortized discount and deferred finance costs on extinguishment of debt																					36,600,000																		7,600,000
Payment of premiums and third-party expenses																					9,700,000																		71,400,000
Period with no maturities of long-term debt (in years)																		5
Principal amount due between 2018 and 2021																		$ 1,781,000,000