Long-Term Debt (Details Textuals)			1 Months Ended						2 Months Ended	3 Months Ended	12 Months Ended
		Apr. 30, 2014 USD ($)	Aug. 31, 2018 USD ($)	Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2016 USD ($) shares	Feb. 28, 2013 USD ($)	Feb. 28, 2011 USD ($)	Jan. 31, 2018 USD ($)	Jun. 30, 2018 USD ($) shares	Dec. 31, 2018 USD ($) shares		Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Aug. 13, 2018 USD ($)	May 30, 2018 USD ($)	Apr. 18, 2018 USD ($)
Senior Secured Bank Credit Facility [Abstract]
Borrowing base											$ 615,000,000				$ 1,050,000,000.00
Lender commitments											615,000,000				1,050,000,000
Maximum incurrence of junior lien debt permitted											$ 1,650,000,000.00				$ 1,200,000,000.0
Maximum senior secured debt to consolidated EBITDAX requirement											2.5
Minimum EBITDAX to consolidated interest requirement											1.25
Current ratio requirement											1.0
Senior Secured Bank Credit Agreement					$ 475,000,000						$ 0		$ 475,000,000
Long Term Debt (Textuals) [Abstract]
Interest in guarantor subsidiaries											100.00%
Debt Exchange, Amount					609,800,000	$ 1,057,800,000
Extinguishment of Debt, Amount				$ 40,800,000	143,600,000	$ 442,900,000
Future interest on 2022 Senior Secured Notes					316,818,000						$ 250,218,000	[1]	316,818,000
Gain (loss) on extinguishment of debt											$ 0		0	$ 115,095,000
Debt Instrument, Repurchased Face Amount														181,900,000
Debt Instrument, Repurchase Amount														76,700,000
Lease period included in long term transportation service agreement											20 years
Unamortized debt issuance costs					(13,800,000)						$ (19,100,000)		(13,800,000)
Convertible Debt [Abstract]
Issued as part of debt exchange, shares | shares						40,729,332.000000
Issued pursuant to notes conversion, value											$ 162,004,000		0	$ 0
Common Stock
Convertible Debt [Abstract]
Issued as part of debt exchange, shares | shares														40,729,332
Issued pursuant to notes conversion, shares | shares										55,249,955.000000	55,249,955
Issued pursuant to notes conversion, value											$ 55,000
9% Senior Secured Second Lien Notes due 2021
Long Term Debt (Textuals) [Abstract]
Face value of notes						$ 614,900,000
Debt Instrument, Interest Rate, Stated Percentage											9.00%
Selling Price Of Debt Instrument						100.00%
9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Face value of notes				74,100,000	381,568,000				$ 74,100,000				381,568,000
Debt Instrument, Interest Rate, Stated Percentage											9.25%
Selling Price Of Debt Instrument									100.00%
7 1/2% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Face value of notes			$ 450,000,000.0
Debt Instrument, Interest Rate, Stated Percentage											7.50%
Selling Price Of Debt Instrument			100.00%
3 1/2% Convertible Senior Notes due 2024
Long Term Debt (Textuals) [Abstract]
Face value of notes					84,650,000								$ 84,650,000
Debt instrument, amount exchanged										$ 84,700,000
Convertible Debt																	$ 0.0
Debt Instrument, Interest Rate, Stated Percentage											3.50%
Convertible Debt [Abstract]
Debt instrument, amount exchanged										84,700,000
5% Convertible Senior Notes due 2023
Long Term Debt (Textuals) [Abstract]
Face value of notes				59,400,000					$ 59,400,000
Debt instrument, amount exchanged										59,400,000
Convertible Debt																$ 0.0
Convertible Debt [Abstract]
Debt instrument, amount exchanged										$ 59,400,000
6 3/8% Senior Subordinated Notes due 2021
Long Term Debt (Textuals) [Abstract]
Debt Exchange, Amount				11,600,000
Face value of notes								$ 400,000,000
Debt Instrument, Interest Rate, Stated Percentage											6.375%
Selling Price Of Debt Instrument								100.00%
Debt Instrument, Repurchased Face Amount														$ 9,800,000
5 1/2% Senior Subordinated Notes due 2022
Long Term Debt (Textuals) [Abstract]
Debt Exchange, Amount				94,200,000	364,000,000
Face value of notes		$ 1,250,000,000.00
Debt Instrument, Interest Rate, Stated Percentage											5.50%
Selling Price Of Debt Instrument		100.00%
Debt Instrument, Repurchased Face Amount														66,100,000
4 5/8% Senior Subordinated Notes due 2023
Long Term Debt (Textuals) [Abstract]
Debt Exchange, Amount				68,500,000	$ 245,800,000
Face value of notes							$ 1,200,000,000.0
Debt Instrument, Interest Rate, Stated Percentage											4.625%
Selling Price Of Debt Instrument							100.00%
Debt Instrument, Repurchased Face Amount														106,000,000
Notes Exchange
Long Term Debt (Textuals) [Abstract]
Gain (loss) on extinguishment of debt														12,000,000
Year 2018 | Q4
Senior Secured Bank Credit Facility [Abstract]
Total Debt to Consolidated EBITDAX											5.25
Year 2019
Senior Secured Bank Credit Facility [Abstract]
Total Debt to Consolidated EBITDAX											5.25
Year 2020
Senior Secured Bank Credit Facility [Abstract]
Total Debt to Consolidated EBITDAX											5.25
Year 2021 | Q1
Senior Secured Bank Credit Facility [Abstract]
Total Debt to Consolidated EBITDAX											4.50
Year 2021 | Q2
Senior Secured Bank Credit Facility [Abstract]
Total Debt to Consolidated EBITDAX											4.5
Year 2021 | Q3
Senior Secured Bank Credit Facility [Abstract]
Total Debt to Consolidated EBITDAX											4.5
Debt Instrument, Redemption, Period One | 9% Senior Secured Second Lien Notes due 2021
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											109.00%
Debt Instrument, Redemption, Period One | 9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											109.25%
Debt Instrument, Redemption, Period One | 7 1/2% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											103.75%
Debt Instrument, Redemption, Period One | 6 3/8% Senior Subordinated Notes due 2021
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											101.062%
Debt Instrument, Redemption, Period One | 5 1/2% Senior Subordinated Notes due 2022
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											102.75%
Debt Instrument, Redemption, Period One | 4 5/8% Senior Subordinated Notes due 2023
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											101.542%
Initial Redemption Period With Proceeds From Equity Offering Member | 9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											109.25%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed											35.00%
Initial Redemption Period With Proceeds From Equity Offering Member | 7 1/2% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											107.50%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed											35.00%
Initial Redemption Period with Make-Whole Premium | 9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											100.00%
Initial Redemption Period with Make-Whole Premium | 7 1/2% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage											100.00%
Senior Secured Bank Credit Facility
Senior Secured Bank Credit Facility [Abstract]
Credit facility, unused capacity - commitment fee percentage											0.50%
Credit facility - weighted average interest rate													4.50%
Senior Secured Bank Credit Facility | Letter of Credit
Senior Secured Bank Credit Facility [Abstract]
Borrowing capacity under line of credit facility designated for a specific purpose											$ 100,000,000
Senior Secured Bank Credit Facility | Swingline Loan
Senior Secured Bank Credit Facility [Abstract]
Borrowing capacity under line of credit facility designated for a specific purpose											$ 25,000,000
Senior Secured Bank Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility											2.75%
Senior Secured Bank Credit Facility | London Interbank Offered Rate (LIBOR) | Maximum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility											3.75%
Senior Secured Bank Credit Facility | Base Rate | Minimum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility											1.75%
Senior Secured Bank Credit Facility | Base Rate | Maximum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility											2.75%
Secured Debt
Long Term Debt (Textuals) [Abstract]
Maximum total debt to EBITDA requirement											2.5
Senior Subordinated Notes
Long Term Debt (Textuals) [Abstract]
Debt Exchange, Amount				$ 174,300,000
Gain (loss) on extinguishment of debt														$ 103,100,000
Senior Subordinated Notes | 4 5/8% Senior Subordinated Notes due 2023
Long Term Debt (Textuals) [Abstract]
Maximum total debt to EBITDA requirement											2.5
Notes Exchange
Long Term Debt (Textuals) [Abstract]
Future interest on 2022 Senior Secured Notes	[1]										$ 113,800,000
Interest payable											$ 23,200,000

[1] Future interest payable represents most of the interest due over the term of our 9% Senior Secured Second Lien Notes due 2021 (the “2021 Senior Secured Notes”), 9¼% Senior Secured Second Lien Notes due 2022 (the “2022 Senior Secured Notes”) and to a small extent our previously outstanding 3½% Convertible Senior Notes due 2024 (the “2024 Convertible Senior Notes”) and has been accounted for as debt in accordance with FASC 470-60, Troubled Debt Restructuring by Debtors. Our current maturities of long-term debt as of December 31, 2018 include $85.3 million of future interest payable related to the 2021 Senior Secured Notes and 2022 Senior Secured Notes that is due within the next twelve months. See January 2018 Senior Subordinated Note Exchanges and 2017 Senior Subordinated Note Exchanges below for further discussion.