Long-Term Debt (Details 2) (USD $)	3 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended	1 Months Ended				3 Months Ended			1 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Jan. 31, 2013 4.75% convertible senior notes due January 2014	Mar. 31, 2013 4.75% convertible senior notes due January 2014	Dec. 31, 2012 4.75% convertible senior notes due January 2014	Mar. 31, 2013 Partnership's senior notes due 2021	Mar. 31, 2013 Partnership's senior notes due 2021	Mar. 31, 2013 Partnership's senior notes due 2021 Prior to April 1, 2016 item	Mar. 31, 2013 Partnership's senior notes due 2021 Twelve month period beginning April 1, 2017	Mar. 31, 2013 Partnership's senior notes due 2021 Twelve month period beginning April 1, 2018	Mar. 31, 2013 Partnership's senior notes due 2021 Beginning April 1, 2019 and thereafter	Mar. 31, 2013 4.25% convertible senior notes due June 2014	Dec. 31, 2012 4.25% convertible senior notes due June 2014	Jun. 30, 2009 4.25% convertible senior notes due June 2014	Mar. 31, 2012 Revolving credit facility due July 2016	Mar. 31, 2012 Revolving credit facility due July 2016	Mar. 31, 2013 Revolving credit facility due July 2016	Mar. 31, 2013 Partnership's revolving credit facility and term loan facility	Mar. 31, 2013 Partnership's revolving credit facility and term loan facility	Mar. 31, 2012 Partnership's revolving credit facility and term loan facility	Mar. 31, 2013 Partnership's revolving credit facility	Mar. 31, 2012 Partnership's revolving credit facility	Mar. 31, 2013 Partnership's term loan facility
Long-term Debt
Repayment of long term debt	$ 1,145,251,000	$ 913,048,000	$ 143,800,000
Interest rate (as a percent)			4.75%		4.75%	6.00%	6.00%					4.25%	4.25%
Redemption price as percentage of principal amount			100.00%					106.00%	103.00%	101.50%	100.00%
Increase (decrease) in borrowing capacity															(200,000,000)						(100,000,000)	200,000,000
Revolving credit facility borrowing capacity															900,000,000	900,000,000					650,000,000	750,000,000
Write-off of deferred financing costs				900,000												1,300,000		700,000
Decrease in applicable margin (as a percent)																					0.25%		0.50%
Outstanding borrowings																	220,500,000
Outstanding letters of credit																	173,800,000
Initial conversion rate of debt instrument (Shares per USD)												0.0431951
Initial conversion price per common stock shares (in dollars per share)												$ 23.15
Undrawn capacity under revolving credit facility																	505,700,000				412,000,000
Available borrowings under revolving credit facility																	505,700,000				412,000,000
Maximum total debt to EBITDA ratio																		5.25
Maximum revised total debt to EBITDA ratio																		5.5
Revised total debt to EBITDA ratio, applicable period after acquisition																		6 months
Maximum senior secured debt to EBITDA ratio																		4.0
Principle amount of senior notes						350,000,000	350,000,000							355,000,000
Amount by which value of shares converted exceeds principle												59,000,000
Proceeds from borrowings of long-term debt	1,204,037,000	844,500,000				336,900,000
Amount of unamortized discount of notes						5,500,000	5,500,000					28,800,000	34,300,000
Effective interest rate (as a percent)						6.25%	6.25%
Transaction costs							$ 7,600,000												$ 4,300,000	$ 500,000
Maximum period in which the entity is required to register the Notes						365 days
Maximum percentage of the aggregate principal amount of debt instruments that may be redeemed prior to 2016								35.00%
Number of equity offerings								1
Minimum notes remaining outstanding if notes redeemed prior to 2016 (as a percent)								65.00%
Maximum number of days within which the entity may redeem a percentage of the note following the date of the closing of equity offering								180 days