Long-Term Debt (Details) $ in Thousands		1 Months Ended			3 Months Ended			5 Months Ended	9 Months Ended		12 Months Ended
	Mar. 20, 2014 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jan. 31, 2015	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Nov. 30, 2014 USD ($)	Mar. 19, 2014 USD ($)
Long-Term Debt
Long-term debt, net of discounts					$ 4,755,352				$ 4,755,352		$ 3,621,404
Deferred financing costs									20,558	$ 2,045
Pre-tax loss related to repurchase of Senior Notes					(29)		$ 0		(117,889)	0
Non-cash write-off of the unamortized discount and deferred finance costs						$ 14,700
Payment of redemption premiums and third-party expenses						103,200
Accrued Liabilities
Long-Term Debt
Accrued interest payable					57,900				57,900
Revolving credit facility
Long-Term Debt
Long-term debt, net of discounts					662,000				662,000		$ 97,600
Applicable interest rate (as a percent)											4.50%
Credit facility current lending capacity	$ 1,300,000
Extension of maturity	18 months
Accordion option to increase borrowing capacity under the Credit Facility	$ 500,000												$ 250,000
Deferred financing costs										$ 2,000
Letters of credit maximum borrowing capacity					150,000				150,000
Short-term swingline loan maximum borrowing capacity					10,000				$ 10,000
Minimum Interest Coverage Ratio									2.5
Maximum leverage ratio prior to Collateral Release Date				5.25				5.5			5.5
Maximum leverage ratio after Collateral Release Date									5.00
Borrowings outstanding					662,000				$ 662,000
Letters of credit outstanding amount					8,300				8,300
Unused borrowing capacity					629,700				$ 629,700
Revolving credit facility | Alternate Base Rate Loans | Minimum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)									0.50%
Margin after Collateral Release Date (as a percent)									0.125%
Revolving credit facility | Alternate Base Rate Loans | Maximum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)									1.50%
Margin after Collateral Release Date (as a percent)									1.00%
Revolving credit facility | Alternate Base Rate Loans | Prime rate
Long-Term Debt
Basis of variable interest rate									prime rate
Revolving credit facility | Alternate Base Rate Loans | Federal funds effective swap rate
Long-Term Debt
Basis of variable interest rate									Federal Funds Rate
Spread on variable rate basis (as a percent)									0.50%
Revolving credit facility | Alternate Base Rate Loans | One month LIBOR
Long-Term Debt
Basis of variable interest rate									One month LIBOR
Spread on variable rate basis (as a percent)									1.00%
Revolving credit facility | LIBO Rate Loans | Minimum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)									1.50%
Margin after Collateral Release Date (as a percent)									1.125%
Revolving credit facility | LIBO Rate Loans | Maximum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)									2.50%
Margin after Collateral Release Date (as a percent)									2.00%
Revolving credit facility | LIBO Rate Loans | One month LIBOR
Long-Term Debt
Basis of variable interest rate									LIBOR
Revolving credit facility | Credit facility borrowings at 2.5%
Long-Term Debt
Long-term debt, net of discounts					$ 300,000				$ 300,000
Applicable interest rate (as a percent)					2.50%				2.50%
Revolving credit facility | Credit facility borrowings at 4.5%
Long-Term Debt
Long-term debt, net of discounts					$ 362,000				$ 362,000
Applicable interest rate (as a percent)					4.50%				4.50%
Senior Notes
Long-Term Debt
Estimated aggregate fair value of debt					$ 3,820,000				$ 3,820,000		$ 3,563,000
Senior Notes | 2020 Senior Notes, 6.75% interest, issued November 2010 and due November 2020
Long-Term Debt
Long-term debt, net of discounts											$ 500,000
Debt instrument, stated interest rate percentage											6.75%
Amount of debt repurchased		$ 500,000
Senior Notes | 2021 Senior Notes, 6.5% interest, issued February and March 2011 and due August 2021
Long-Term Debt
Long-term debt, net of discounts											$ 324,587
Debt instrument, stated interest rate percentage											6.50%
Long-term debt, discounts											$ 413
Amount of debt repurchased		325,000
Senior Notes | 2022 Senior Notes, 6.25% interest, issued October 2011 and due June 2022
Long-Term Debt
Long-term debt, net of discounts											$ 455,000
Debt instrument, stated interest rate percentage											6.25%
Amount of debt repurchased		455,000
Senior Notes | 2023A Senior Notes, 5.5% interest, issued August 2012 and due February 2023
Long-Term Debt
Long-term debt, net of discounts					$ 744,720				$ 744,720		$ 744,217
Debt instrument, stated interest rate percentage					5.50%				5.50%
Long-term debt, discounts					$ 5,280				$ 5,280		5,783
Senior Notes | 2023B Senior Notes, 4.5% interest, issued January 2013 and due July 2023
Long-Term Debt
Long-term debt, net of discounts					$ 1,000,000				$ 1,000,000		1,000,000
Debt instrument, stated interest rate percentage					4.50%				4.50%
Senior Notes | 2024 Senior Notes, 4.875% interest, issued November 2014 and March 2015, due December 2024
Long-Term Debt
Long-term debt, net of discounts					$ 1,159,934				$ 1,159,934		$ 500,000
Debt instrument, stated interest rate percentage					4.875%				4.875%
Long-term debt, premium					$ 9,934				$ 9,934
Senior Notes | 2024 Senior Notes, 4.875% interest, issued March 2015 and due December 2024
Long-Term Debt
Debt instrument, stated interest rate percentage			4.875%
Aggregate principal amount			$ 650,000
Proceeds from issuance of senior notes, net of underwriting fees and the other expenses of the offering			653,600
Accrued interest on notes issued			$ 9,000
Senior Notes | 2024 Senior Notes, 4.875% interest, issued November 2014 and due December 2024
Long-Term Debt
Debt instrument, stated interest rate percentage												4.875%
Aggregate principal amount												$ 500,000
Senior Notes | 2025 Senior Notes, 4.875% interest, issued June 2015 and due June 2025
Long-Term Debt
Long-term debt, net of discounts					$ 1,188,698				$ 1,188,698
Debt instrument, stated interest rate percentage					4.875%				4.875%
Long-term debt, discounts					$ 11,302				$ 11,302
Aggregate principal amount		1,200,000				$ 1,200,000		$ 1,200,000
Proceeds from issuance of senior notes, net of underwriting fees and the other expenses of the offering		1,174,900
Accrued interest on notes issued		$ 23,000