Long-Term Debt (Details Textuals)			1 Months Ended						2 Months Ended	12 Months Ended
		Apr. 30, 2014 USD ($)	Jan. 31, 2018 USD ($) D $ / shares	Dec. 31, 2017 USD ($) shares D $ / shares		May 31, 2016 USD ($) shares	Feb. 28, 2013 USD ($)	Feb. 28, 2011 USD ($)	Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares		Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
Long Term Debt (Textuals) [Abstract]
Interest in guarantor subsidiaries				100.00%						100.00%
Debt Instrument, Amount Exchanged				$ 609,800,000		$ 1,057,800,000
Senior Secured Second Lien Notes						614,900,000
Convertible Debt				84,650,000						$ 84,650,000		$ 0
Extinguishment of Debt, Amount				143,600,000		$ 442,900,000
Future interest on 2022 Senior Secured Notes and 2024 Convertible Senior Notes				316,818,000	[1]					316,818,000	[1]	228,825,000
Gain (loss) on extinguishment of debt										$ 0		115,095,000	$ 0
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)						$ (13,800,000)		$ (24,700,000)
Common stock issued as part of debt exchanges | shares				402,549,346		40,700,000				402,549,346		402,334,655
Subsequent Event
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Amount Exchanged			$ 174,300,000
Extinguishment of Debt, Amount			$ 40,800,000
Notes Exchange
Long Term Debt (Textuals) [Abstract]
Future interest on 2022 Senior Secured Notes and 2024 Convertible Senior Notes	[1]			$ 138,300,000						$ 138,300,000
Gain (loss) on extinguishment of debt												$ 12,000,000
Interest payable				$ 32,300,000						$ 32,300,000
3 1/2% Convertible Senior Notes Due 2024
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Interest Rate, Stated Percentage				3.50%						3.50%
Selling Price Of Debt Instrument				100.00%
Volume weighted average stock price for automatic conversion | $ / shares				$ 2.65
Threshold trading days for automatic debt conversion | D				10
Consecutive trading days threshold for automatic debt conversion | D				15
3 1/2% Convertible Senior Notes Due 2024 | Conversion Period One
Long Term Debt (Textuals) [Abstract]
Share conversion rate per $1,000 principal				455.56
3 1/2% Convertible Senior Notes Due 2024 | Conversion Period Two
Long Term Debt (Textuals) [Abstract]
Share conversion rate per $1,000 principal				444.44
3 1/2% Convertible Senior Notes Due 2024 | Automatic Conversion Period
Long Term Debt (Textuals) [Abstract]
Share conversion rate per $1,000 principal				444.44
5% Convertible Senior Notes Due 2023 | Subsequent Event
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Interest Rate, Stated Percentage			5.00%						5.00%
Share conversion rate per $1,000 principal			281.69
Volume weighted average stock price for automatic conversion | $ / shares			$ 3.55
Threshold trading days for automatic debt conversion | D			10
Consecutive trading days threshold for automatic debt conversion | D			15
5% Convertible Senior Notes Due 2023 | Subsequent Event | Board of Directors Conversion Increase Option
Long Term Debt (Textuals) [Abstract]
Share conversion rate per $1,000 principal			393.55
Senior Secured Bank Credit Facility
Senior Secured Bank Credit Facility [Abstract]
Borrowing base				$ 1,050,000,000.00						$ 1,050,000,000.00
Lender commitments				1,050,000,000.00						$ 1,050,000,000.00
EBITDAX to Consolidated Interest										1.25
Current Ratio Requirement										1.0
Credit facility, unused capacity - commitment fee percentage										0.50%
Credit facility - weighted average interest rate										4.50%		3.00%
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						$ 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						$ 25,000,000
Secured Debt
Long Term Debt (Textuals) [Abstract]
Total Debt to EBITDA requirement										2.5
Secured Debt | 9% Senior Secured Second Lien Notes due 2021
Long Term Debt (Textuals) [Abstract]
Senior Secured Second Lien Notes				$ 614,919,000						$ 614,919,000		$ 614,919,000
Debt Instrument, Interest Rate, Stated Percentage				9.00%						9.00%
Selling Price Of Debt Instrument						100.00%
Secured Debt | 9% Senior Secured Second Lien Notes due 2021 | Debt Instrument, Redemption, Period One
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										109.00%
Secured Debt | 9% Senior Secured Second Lien Notes due 2021 | Initial Redemption Period With Proceeds From Equity Offering Member
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										109.00%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed										35.00%
Secured Debt | 9% Senior Secured Second Lien Notes due 2021 | Initial Redemption Period with Make-Whole Premium
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										100.00%
Secured Debt | 9 1/4% Senior Secured Second Lien Notes Due 2022
Long Term Debt (Textuals) [Abstract]
Senior Secured Second Lien Notes				$ 381,568,000						$ 381,568,000		0
Debt Instrument, Interest Rate, Stated Percentage				9.25%						9.25%
Secured Debt | 9 1/4% Senior Secured Second Lien Notes Due 2022 | Subsequent Event
Long Term Debt (Textuals) [Abstract]
Face value of notes			$ 74,100,000						$ 74,100,000
Selling Price Of Debt Instrument									100.00%
Secured Debt | 9 1/4% Senior Secured Second Lien Notes Due 2022 | Debt Instrument, Redemption, Period One
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										109.25%
Secured Debt | 9 1/4% Senior Secured Second Lien Notes Due 2022 | Initial Redemption Period With Proceeds From Equity Offering Member
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										109.25%
Debt Instrument, Percentage of Principal Amount Available To Be Redeemed										35.00%
Secured Debt | 9 1/4% Senior Secured Second Lien Notes Due 2022 | Initial Redemption Period with Make-Whole Premium
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										100.00%
Convertible Debt
Long Term Debt (Textuals) [Abstract]
Total Debt to EBITDA requirement										2.5
Convertible Debt | 5% Convertible Senior Notes Due 2023 | Subsequent Event
Long Term Debt (Textuals) [Abstract]
Face value of notes			$ 59,400,000						$ 59,400,000
Debt Instrument, Interest Rate, Stated Percentage			5.00%						5.00%
Selling Price Of Debt Instrument			100.00%
Senior Subordinated Notes
Long Term Debt (Textuals) [Abstract]
Gain (loss) on extinguishment of debt												103,100,000
Senior Subordinated Notes | 6 3/8% Senior Subordinated Notes due 2021
Long Term Debt (Textuals) [Abstract]
Face value of notes								$ 400,000,000
Debt Instrument, Interest Rate, Stated Percentage				6.375%						6.375%
Selling Price Of Debt Instrument								100.00%
Debt Instrument, Repurchased Face Amount												9,800,000
Senior Subordinated Notes | 6 3/8% Senior Subordinated Notes due 2021 | Subsequent Event
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Amount Exchanged			$ 11,600,000
Senior Subordinated Notes | 6 3/8% Senior Subordinated Notes due 2021 | Debt Instrument, Redemption, Period One
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										102.125%
Senior Subordinated Notes | 5 1/2% Senior Subordinated Notes due 2022
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Amount Exchanged				$ 364,000,000
Face value of notes		$ 1,250,000,000.00
Debt Instrument, Interest Rate, Stated Percentage				5.50%						5.50%
Selling Price Of Debt Instrument		100.00%
Total Debt to EBITDA requirement										2.5
Debt Instrument, Repurchased Face Amount												66,100,000
Senior Subordinated Notes | 5 1/2% Senior Subordinated Notes due 2022 | Subsequent Event
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Amount Exchanged			94,200,000
Senior Subordinated Notes | 5 1/2% Senior Subordinated Notes due 2022 | Debt Instrument, Redemption, Period One
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										104.125%
Senior Subordinated Notes | 4 5/8% Senior Subordinated Notes due 2023
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Amount Exchanged				$ 245,800,000
Face value of notes							$ 1,200,000,000.0
Debt Instrument, Interest Rate, Stated Percentage				4.625%						4.625%
Selling Price Of Debt Instrument							100.00%
Total Debt to EBITDA requirement										2.5
Debt Instrument, Repurchased Face Amount												$ 106,000,000
Senior Subordinated Notes | 4 5/8% Senior Subordinated Notes due 2023 | Subsequent Event
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Amount Exchanged			$ 68,500,000
Senior Subordinated Notes | 4 5/8% Senior Subordinated Notes due 2023 | Debt Instrument, Redemption, Period One
Long Term Debt (Textuals) [Abstract]
Debt Instrument, Redemption Price, Percentage										102.313%
Year 2018 | Q1
Senior Secured Bank Credit Facility [Abstract]
Senior Secured Debt to Consolidated EBITDAX										3.0
Year 2018 | Q2
Senior Secured Bank Credit Facility [Abstract]
Senior Secured Debt to Consolidated EBITDAX										2.5
Year 2018 | Q3
Senior Secured Bank Credit Facility [Abstract]
Senior Secured Debt to Consolidated EBITDAX										2.5
Year 2018 | Q4
Senior Secured Bank Credit Facility [Abstract]
Senior Secured Debt to Consolidated EBITDAX										2.5
Year 2019 | Q1
Senior Secured Bank Credit Facility [Abstract]
Senior Secured Debt to Consolidated EBITDAX										2.5
Year 2019 | Q2
Senior Secured Bank Credit Facility [Abstract]
Senior Secured Debt to Consolidated EBITDAX										2.5
Year 2019 | Q3
Senior Secured Bank Credit Facility [Abstract]
Senior Secured Debt to Consolidated EBITDAX										2.5
Minimum
Long Term Debt (Textuals) [Abstract]
Total shares issued upon conversion | shares				38,000,000
Maximum
Long Term Debt (Textuals) [Abstract]
Total shares issued upon conversion | shares				39,000,000
London Interbank Offered Rate (LIBOR) | Minimum | Senior Secured Bank Credit Facility
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on Senior Secured Bank Credit Facility										2.50%
London Interbank Offered Rate (LIBOR) | Maximum | Senior Secured Bank Credit Facility
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on Senior Secured Bank Credit Facility										3.50%
Base Rate | Minimum | Senior Secured Bank Credit Facility
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on Senior Secured Bank Credit Facility										1.50%
Base Rate | Maximum | Senior Secured Bank Credit Facility
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on Senior Secured Bank Credit Facility										2.50%

[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 3½% Convertible Senior Notes due 2024 (the “2024 Convertible Senior Notes”), which 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, 2017 include $75.3 million of future interest payable related to these notes that is due within the next twelve months. See December 2017 and January 2018 Note Exchanges below for further discussion.