Long-Term Debt (Details Textuals) (USD $)	3 Months Ended	12 Months Ended			0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended
	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Feb. 28, 2011	Apr. 30, 2014	Feb. 28, 2013	May 30, 2014
Debt Instruments [Abstract]
Loss on early extinguishment of debt	$ 113,900,000	$ 113,908,000	$ 44,651,000	$ 0
Interest in guarantor subsidiaries		100.00%			100.00%
Lease period included in long term transportation service agreement		20 years
Unamortized debt issuance costs		57,300,000	58,900,000		57,300,000
Bank Credit Agreement [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Line of Credit, Borrowing Base		3,000,000,000.0			3,000,000,000.0
Line of Credit Facility, Current Borrowing Capacity		1,600,000,000.0			1,600,000,000.0
Bank Credit Agreement restriction, limitation on sale of borrowing base properties		10.00%			10.00%
Total Debt to EBITDAX Requirement		4.25
Current Ratio Requirement		1.0
Minimum Bank Credit Facility Availability Percentage To Pay Distributions		10.00%
Line of Credit Facility, Interest Rate During Period					1.90%
Bank Credit Agreement [Member] | Letter of Credit [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Line of Credit Facility, Capacity Available for Specific Purpose		50,000,000			50,000,000
Bank Credit Agreement [Member] | Swingline Loan [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Line of Credit Facility, Capacity Available for Specific Purpose		25,000,000			25,000,000
9 1/2% Senior Subordinated Notes due 2016 [Member]
Debt Instruments [Abstract]
Debt Instrument, Repurchased Face Amount			224,900,000
9 3/4% Senior Subordinated Notes due 2016 [Member]
Debt Instruments [Abstract]
Debt Instrument, Repurchased Face Amount			426,400,000
8 1/4% Senior Subordinated Notes due 2020 [Member]
Debt Instruments [Abstract]
Interest rate on senior subordinated notes		8.25%			8.25%
Debt Instrument, Repurchased Face Amount							815,200,000		181,100,000
Debt Instrument Redemption Price Percentage Exclusive of Make Whole Premium									100.00%
6 3/8% Senior Subordinated Notes due 2021 [Member]
Debt Instruments [Abstract]
Face value of senior subordinated notes						400,000,000
Interest rate on senior subordinated notes		6.375%			6.375%
Selling Price Of Debt Instrument						100.00%
6 3/8% Senior Subordinated Notes due 2021 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		103.188%
6 3/8% Senior Subordinated Notes due 2021 [Member] | Initial Redemption Period with Make-Whole Premium [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		100.00%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed		100.00%
5 1/2% Senior Subordinated Notes Due 2022 [Member]
Debt Instruments [Abstract]
Face value of senior subordinated notes							1,250,000,000.00
Interest rate on senior subordinated notes		5.50%			5.50%
Proceeds from issuance of subordinated long-term debt, net of commissions and fees							1,230,000,000
Selling Price Of Debt Instrument							100.00%
Total Debt to EBITDA Requirement		2.5
5 1/2% Senior Subordinated Notes Due 2022 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		104.125%
5 1/2% Senior Subordinated Notes Due 2022 [Member] | Initial Redemption Period with Proceeds from Equity Offering [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		105.50%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed		35.00%
5 1/2% Senior Subordinated Notes Due 2022 [Member] | Initial Redemption Period with Make-Whole Premium [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		100.00%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed		100.00%
4 5/8% Senior Subordinated Notes due 2023 [Member]
Debt Instruments [Abstract]
Face value of senior subordinated notes								1,200,000,000.0
Interest rate on senior subordinated notes		4.625%			4.625%
Proceeds from issuance of subordinated long-term debt, net of commissions and fees								$ 1,180,000,000
Selling Price Of Debt Instrument								100.00%
Total Debt to EBITDA Requirement		2.5
4 5/8% Senior Subordinated Notes due 2023 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		102.313%
4 5/8% Senior Subordinated Notes due 2023 [Member] | Initial Redemption Period with Proceeds from Equity Offering [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		104.625%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed		35.00%
4 5/8% Senior Subordinated Notes due 2023 [Member] | Initial Redemption Period with Make-Whole Premium [Member]
Debt Instruments [Abstract]
Debt Instrument, Redemption Price, Percentage		100.00%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed		100.00%
Minimum [Member] | Bank Credit Agreement [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.30%
Maximum [Member] | Bank Credit Agreement [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.375%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Bank Credit Agreement [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Interest rate margins on Bank Credit Agreement		1.25%
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Bank Credit Agreement [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Interest rate margins on Bank Credit Agreement		2.25%
Base Rate [Member] | Minimum [Member] | Bank Credit Agreement [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Interest rate margins on Bank Credit Agreement		0.25%
Base Rate [Member] | Maximum [Member] | Bank Credit Agreement [Member]
$1.6 Billion Revolving Credit Agreement [Abstract]
Interest rate margins on Bank Credit Agreement		1.25%