Long-Term Debt - Narrative (Details) $ / shares in Units, shares in Millions			1 Months Ended		3 Months Ended				9 Months Ended
		Jun. 10, 2015 USD ($)	Aug. 31, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) shares		Jun. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)		Sep. 30, 2014 USD ($)	Aug. 13, 2015 USD ($)	Jun. 09, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument
Write off of debt issuance costs									$ 7,108,000		$ 0
Carrying Value					$ 3,936,994,000				3,936,994,000					$ 3,195,436,000
Common stock issued for debt exchange (in shares) | shares					8.0
Aggregate principal amount of convertible senior notes issued in debt exchange									35,147,000		0
Gain (loss) on extinguishment of debt					$ 340,699,000			$ 0	$ 358,633,000		$ 0
Aggregate cash payments for early conversion					$ 2,700,000
8.125% Convertible Senior Notes due 2022
Debt Instrument
Long-term debt, fixed interest rate					8.125%				8.125%
7.5% Convertible Senior Notes due 2023
Debt Instrument
Long-term debt, fixed interest rate					7.50%				7.50%
Senior credit facility
Debt Instrument
Borrowing base													$ 900,000,000
June Amendment | Senior credit facility
Debt Instrument
Maximum borrowing capacity		$ 1,000,000,000.0
Borrowing base					$ 500,000,000				$ 500,000,000
Write off of debt issuance costs		4,900,000
Additional aggregate principal indebtedness permitted (less than)		1,750,000,000.00
Reduction in borrowing base for every $1 junior lien debt incurred		$ 0.25
August 2015 Amendment | Senior credit facility
Debt Instrument
Allowed repurchases of outstanding debt												$ 200,000,000
Senior credit facility
Debt Instrument
Covenant ratio of secured debt To EBITDA, maximum													2.25
Covenant, Ratio of EBITDA to interest expense at Mar 2015													2.00
Covenant, Ratio of EBITDA to interest expense at Jun 2015													2.00
Covenant, Ratio of EBITDA to interest expense at Sep 2015													1.75
Covenant, Ratio of EBITDA to interest expense at Dec 2015													1.50
Covenant, Ratio of EBITDA to interest expense at Mar 2016													1.50
Covenant, Ratio of EBITDA to interest expense at June 2016													1.50
Covenant, Ratio of EBITDA to interest expense at Sep 2016													1.50
Covenant, Ratio of EBITDA to interest expense at Dec 2016													2.00
Current assets to current liabilities, ratio minimum													1.00
Covenant, Ratio of total net debt to EBITDA at Jun 2016													6.25
Covenant, Ratio of total net debt to EBITDA at Sep 2016													6.00
Covenant, Ratio of total net debt to EBITDA at Dec 2016													6.00
Covenant, Ratio of total net debt to EBITDA at Mar 2017													5.50
Covenant, Ratio of total net debt to EBITDA at Jun 2017													5.50
Covenant, Ratio of total net debt to EBITDA at Sep 2017													5.00
Covenant, Ratio of total net debt to EBITDA at Dec 2017													5.00
Covenant, Ratio of total net debt to EBITDA at Mar 2018													4.50
Outstanding letters of credit					$ 11,000,000				$ 11,000,000
Senior credit facility | June Amendment
Debt Instrument
Covenant ratio of secured debt To EBITDA, maximum					2.00				2.00
Current assets to current liabilities, ratio minimum					1.0				1.0
Minimum collateral amount of proved oil, natural gas and NGL reserves representing the discounted present value of reserves used in borrowing base determination		80.00%
Senior credit facility | June Amendment | Maximum
Debt Instrument
Unused capacity, commitment fee percentage		0.50%
Senior credit facility | June Amendment | LIBOR | Minimum
Debt Instrument
Basis spread on variable rate		1.75%
Senior credit facility | June Amendment | LIBOR | Maximum
Debt Instrument
Basis spread on variable rate		2.75%
Senior credit facility | June Amendment | Federal Funds Rate
Debt Instrument
Basis spread on variable rate		0.50%
Senior credit facility | June Amendment | One-Month Eurodollar Rate
Debt Instrument
Basis spread on variable rate		1.00%
Senior credit facility | June Amendment | Base Rate | Minimum
Debt Instrument
Basis spread on variable rate		0.75%
Senior credit facility | June Amendment | Base Rate | Maximum
Debt Instrument
Basis spread on variable rate		1.75%
Junior lien debt | June Amendment
Debt Instrument
Outstanding junior debt threshold, reduction of maximum borrowing base		$ 1,500,000,000.00
Senior Secured Notes
Debt Instrument
Debt, face amount				$ 1,250,000,000.0			$ 1,250,000,000.0
Proceeds from issuance of debt, net of issuance costs				$ 1,210,000,000
Long-term debt, fixed interest rate					8.75%				8.75%
Senior Secured Notes | 8.75% Senior Secured Notes due 2020
Debt Instrument
Carrying Value					$ 1,250,000,000				$ 1,250,000,000					0
Long-term debt, fixed interest rate					8.75%				8.75%
Debt issuance costs					$ 39,200,000				$ 39,200,000
Senior Notes
Debt Instrument
Write off of debt issuance costs					3,200,000				3,200,000
Debt issuance costs					57,600,000				57,600,000
Gain (loss) on extinguishment of debt					152,000,000				152,000,000
Aggregate principal amount of debt repurchased			$ 250,000,000
Cash paid to repurchase debt			94,500,000
Notes exchanged/converted			275,000,000
Senior Notes | 8.125% Senior Notes due 2022
Debt Instrument
Carrying Value					$ 601,187,000				$ 601,187,000					$ 750,000,000
Long-term debt, fixed interest rate					8.125%				8.125%					8.125%
Aggregate principal amount of convertible senior notes issued in debt exchange							$ 21,000,000
Aggregate principal amount of debt repurchased			26,100,000
Notes exchanged/converted			101,800,000
Senior Notes | 7.5% Senior Notes due 2021 and 8.125% Senior Notes due 2022
Debt Instrument
Common stock issued for debt exchange (in shares) | shares							28.0
Aggregate principal amount of convertible senior notes issued in debt exchange							$ 50,000,000
Gain (loss) on extinguishment of debt									$ 17,900,000
Notes exchanged/converted									50,000,000
Senior Notes | 7.5% Senior Notes due 2021
Debt Instrument
Carrying Value	[1]				$ 996,309,000				$ 996,309,000					$ 1,178,486,000
Long-term debt, fixed interest rate					7.50%				7.50%					7.50%
Aggregate principal amount of convertible senior notes issued in debt exchange							$ 29,000,000
Aggregate principal amount of debt repurchased			111,600,000
Notes exchanged/converted			40,700,000
Senior Notes | 8.75% Senior Notes due 2020
Debt Instrument
Carrying Value	[2]				$ 401,149,000				$ 401,149,000					$ 445,402,000
Long-term debt, fixed interest rate					8.75%				8.75%					8.75%
Aggregate outstanding principal amount of 8.75% senior notes due 2020 that would adjust maturity date of 8.75% senior secured notes due 2020					$ 100,000,000				$ 100,000,000
Aggregate principal amount of debt repurchased			29,300,000
Notes exchanged/converted			15,900,000
Senior Notes | 7.5% Senior Notes due 2023
Debt Instrument
Carrying Value	[3]				$ 622,923,000				$ 622,923,000					$ 821,548,000
Long-term debt, fixed interest rate					7.50%				7.50%					7.50%
Aggregate principal amount of debt repurchased			83,000,000
Notes exchanged/converted			$ 116,600,000
Convertible Senior Unsecured Notes
Debt Instrument
Write off of debt issuance costs					$ 500,000				$ 500,000
Debt issuance costs					5,900,000				5,900,000
Gain (loss) on extinguishment of debt					(300,000)				(300,000)
Notes exchanged/converted					21,900,000
Conversion rate			0.3636
Percentage of applicable conversion price threshold			40.00%
Conversion price threshold (usd per share) | $ / shares			$ 1.10
Convertible Senior Unsecured Notes | 8.125% Convertible Senior Notes due 2022
Debt Instrument
Carrying Value					$ 36,406,000	[4]			$ 36,406,000	[4]				$ 0
Long-term debt, fixed interest rate			8.125%		8.125%				8.125%
Aggregate principal amount of convertible senior notes issued in debt exchange			$ 158,400,000
Notes exchanged/converted					$ 19,400,000
Aggregate principal amount of convertible debt net of discount and including holders' conversion feature exercised					5,800,000
Convertible Senior Unsecured Notes | 7.5% Convertible Senior Notes due 2023
Debt Instrument
Carrying Value					$ 29,020,000	[5]			$ 29,020,000	[5]				$ 0
Long-term debt, fixed interest rate			7.50%		7.50%				7.50%
Aggregate principal amount of convertible senior notes issued in debt exchange			$ 116,600,000
Notes exchanged/converted					$ 2,500,000
Aggregate principal amount of convertible debt net of discount and including holders' conversion feature exercised					700,000
Senior Notes And Convertible Debt
Debt Instrument
Write off of debt issuance costs					4,000,000				$ 4,000,000
Gain (loss) on extinguishment of debt					$ 189,000,000				$ 189,000,000

[1] Carrying value includes a premium of $2,652 and $3,486 at September 30, 2015 and December 31, 2014, respectively.

[2] Carrying value is net of $3,649 and $4,598 discount at September 30, 2015 and December 31, 2014, respectively.

[3] Carrying value is net of $2,436 and $3,452 discount at September 30, 2015 and December 31, 2014, respectively.

[4] Carrying value includes holder conversion feature liabilities with fair value of $3,113 and is net of $105,691 discount at September 30, 2015.

[5] Carrying value includes holder conversion feature liabilities with fair value of $2,361 and is net of $87,412 discount at September 30, 2015.