Long-Term Debt (Narrative) (Details) (USD $)	1 Months Ended			5 Months Ended	7 Months Ended	12 Months Ended			3 Months Ended	1 Months Ended		1 Months Ended		12 Months Ended		12 Months Ended								1 Months Ended	12 Months Ended
	Oct. 31, 2010	Mar. 31, 2010	May 31, 2009	May 25, 2010	Dec. 31, 2010	Dec. 31, 2011 days	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2010 Senior Notes Due 2013 [Member]	Oct. 31, 2010 Senior Notes Due 2018 [Member]	Oct. 27, 2010 Senior Notes Due 2018 [Member]	May 31, 2010 Senior Notes Due 2016 [Member]	May 31, 2009 Senior Notes Due 2016 [Member]	Dec. 31, 2011 Senior Notes Due 2021 [Member]	May 31, 2011 Senior Notes Due 2021 [Member]	Dec. 31, 2011 Minimum [Member]	Dec. 31, 2011 Maximum [Member]	Dec. 31, 2011 Federal Funds Effective Rate [Member]	Dec. 31, 2011 LIBOR [Member]	Dec. 31, 2011 Base Rate Loans [Member] Minimum [Member]	Dec. 31, 2011 Base Rate Loans [Member] Maximum [Member]	Dec. 31, 2011 Eurodollar Loans [Member] Minimum [Member]	Dec. 31, 2011 Eurodollar Loans [Member] Maximum [Member]	May 31, 2011 Lone Star [Member]	Dec. 31, 2011 Lone Star [Member]	Dec. 31, 2011 ELG [Member]	Dec. 31, 2011 Ranch JV [Member]	Dec. 31, 2011 HPC [Member]	Dec. 31, 2011 Other Affiliates [Member]	Dec. 31, 2011 Redemption After June 1, 2013 [Member] Senior Notes Due 2016 [Member]	Dec. 31, 2011 Redemption Before June 1 2013 [Member] Senior Notes Due 2016 [Member]	Dec. 31, 2011 Redemption Before July 15 2016 [Member] Senior Notes Due 2018 [Member]	Dec. 31, 2011 Redemption Before July 15 2016 [Member] Senior Notes Due 2021 [Member]	Dec. 31, 2011 Redemption After June 1 2014 [Member] Senior Notes Due 2016 [Member]	Dec. 31, 2011 Redemption June 1, 2015 and thereafter [Member] Senior Notes Due 2016 [Member]
Senior notes					$ 856,061,000	$ 1,355,147,000	$ 856,061,000
Additional borrowing under line of credit facility during the year						940,000,000	603,000,000	191,700,000
Repayments to line of credit facility						893,000,000	737,600,000	540,800,000
Amount borrowed under line of credit facility					900,000,000	900,000,000	900,000,000
Capacity available for letters of credit						200,000,000
Revolving credit facility maximum allowable additional borrowings						250,000,000																		150,000,000	550,000,000	250,000,000	50,000,000	250,000,000	250,000,000
Number of Business Days Written Notice Needed For Additional Revolving Commitment Amount						10
Basis spread on variable rate																		0.50%	1.00%	1.50%	2.25%	2.50%	3.25%
Commitment fee percentage on unused capacity of line of credit facility																0.375%	0.50%
Participation fee																2.50%	3.25%
Fronting fee percentage						0.125%
Long-term debt weighted-average interest rate				3.30%	2.96%	3.18%		3.24%
Write off of deferred debt issuance cost		1,800,000
Unamortized loan fees to be capitalized				15,900,000
Maximum percentage of consolidated EBITDA						5.25
Consolidated Interest Expense Ratio						2.75
Secured Debt to Consolidated EBITDA Ratio						3.00
Proceeds from Issuance of Private Placement												236,200,000
Re-measurement of the senior notes										600,000,000	600,000,000		250,000,000		500,000,000
Redeemed senior notes, amount									357,500,000
Loss On Debt Refinancing									17,200,000
Writeoff of unamortized loan fee									5,000,000
Writeoff of unamortized bond premium									6,400,000
Interest percent on senior notes										6.875%			9.375%	6.50%
Capitalized debt issuance costs										$ 12,200,000					$ 9,800,000
Senior notes redemption percentage										35.00%			35.00%	35.00%
Purchase of senior notes	101.00%		101.00%			101.00%				106.875%			109.375%	106.50%																104.688%	100.00%	100.00%	100.00%	102.344%	100.00%
Premium Percentage Applied To Principal Due To Debt Redemption																															1.00%	1.00%	1.00%
Indenture Terms, Days of Rating Decline	90													90
Spread on varaiable rate utilized in determining premium due to debt redemption																															0.50%	0.50%	0.50%