Long-Term Debt (Details Textuals)		1 Months Ended									2 Months Ended	3 Months Ended				12 Months Ended
	Apr. 30, 2014 USD ($)	Jul. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Aug. 31, 2018 USD ($)	Apr. 17, 2018 shares	Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2016 USD ($)	Feb. 28, 2013 USD ($)	Feb. 28, 2011 USD ($)	Jan. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) shares		Sep. 30, 2019 USD ($)	Jun. 30, 2018 USD ($) shares	Dec. 31, 2019 USD ($) shares $ / shares		Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	May 30, 2018 USD ($)	Apr. 18, 2018 USD ($)
Senior Secured Bank Credit Facility [Abstract]
Borrowing base												$ 615,000,000				$ 615,000,000
Lender commitments												615,000,000				$ 615,000,000
Maximum senior secured debt to consolidated EBITDAX requirement																2.5
Minimum EBITDAX to consolidated interest requirement																1.25
Current ratio requirement																1.0
Outstanding borrowings on senior secured bank credit facility												0				$ 0		$ 0
Letters of credit outstanding												$ 87,200,000				$ 87,200,000
Long Term Debt (Textuals) [Abstract]
Interest in guarantor subsidiaries												100.00%				100.00%
Cash paid for debt repurchases or exchanges			$ 120,000,000.0									$ 11,200,000		$ 5,300,000
Gain on extinguishment of debt																$ 155,998,000		0	$ 0
Amount of debt exchanged							$ 609,800,000
Amount of debt extinguished						$ 40,800,000	143,600,000
Debt discount												101,767,000	[1]			101,767,000	[1]	0
Unamortized debt issuance costs												$ 14,000,000.0				$ 14,000,000.0		19,100,000
Convertible debt instrument, number of equity instruments | shares																90,900,000
Lease period included in long-term transportation service agreement																20 years
Convertible Debt [Abstract]
Issued pursuant to notes conversion, shares | shares					55,200,000
Issued pursuant to notes conversion, value															$ 162,000,000.0	$ 0		$ 162,004,000	0
Common Stock
Long Term Debt (Textuals) [Abstract]
Issued as part of debt exchange, shares | shares												38,300,000				36,297,217
Convertible Debt [Abstract]
Issued pursuant to notes conversion, shares | shares															55,200,000			55,249,955
Issued pursuant to notes conversion, value																		$ 55,000
3 1/2% Convertible Senior Notes due 2024
Long Term Debt (Textuals) [Abstract]
Face value of notes							84,700,000												84,700,000
Convertible Debt [Abstract]
Convertible debt instrument, amount exchanged															$ 84,700,000
Convertible debt																					$ 0
5% Convertible Senior Notes due 2023
Long Term Debt (Textuals) [Abstract]
Face value of notes						59,400,000					$ 59,400,000
Convertible Debt [Abstract]
Convertible debt instrument, amount exchanged															$ 59,400,000
Convertible debt																				$ 0
9% Senior Secured Second Lien Notes due 2021
Long Term Debt (Textuals) [Abstract]
Face value of notes								$ 614,900,000
Selling price of debt instrument								100.00%
Stated interest rate percentage												9.00%				9.00%
Carrying amount of long-term debt												$ 614,919,000				$ 614,919,000		614,919,000
9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Face value of notes						74,100,000	381,600,000				$ 74,100,000								$ 381,600,000
Selling price of debt instrument											100.00%
Stated interest rate percentage												9.25%				9.25%
Carrying amount of long-term debt												$ 455,668,000				$ 455,668,000		455,668,000
7 3/4% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Face value of notes		$ 3,800,000	528,000,000.0
Debt discount			$ 22,600,000									$ 27,000,000.0				$ 27,000,000.0
Selling price of debt instrument		100.00%
Stated interest rate percentage												7.75%				7.75%
Fair value percentage of debt principal at issuance date			94.00%
Debt instrument, effective interest rate percentage			9.39%
Carrying amount of long-term debt												$ 531,821,000				$ 531,821,000		0
7 1/2% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Amount of debt exchanged		$ 4,000,000.0
Face value of notes				$ 450,000,000.0
Selling price of debt instrument				100.00%
Stated interest rate percentage												7.50%				7.50%
Carrying amount of long-term debt												$ 20,641,000				$ 20,641,000		450,000,000
6 3/8% Convertible Senior Notes due 2024
Long Term Debt (Textuals) [Abstract]
Face value of notes			$ 245,500,000
Debt discount			$ 79,900,000									$ 74,800,000				$ 74,800,000
Stated interest rate percentage												6.375%				6.375%
Fair value percentage of debt principal at issuance date			67.00%
Debt instrument, effective interest rate percentage			15.31%
Carrying amount of long-term debt												$ 245,548,000				$ 245,548,000		0
Convertible debt instrument, conversion ratio																370
Convertible debt instrument, number of equity instruments																90,900,000
Convertible debt instrument, stock price trigger | $ / shares																$ 2.43
Convertible debt instrument, threshold trading days																10
Convertible debt instrument, threshold consecutive trading days																15
6 3/8% Senior Subordinated Notes due 2021
Long Term Debt (Textuals) [Abstract]
Amount of debt exchanged			$ 152,200,000			11,600,000
Face value of notes										$ 400,000,000
Selling price of debt instrument										100.00%
Stated interest rate percentage												6.375%				6.375%
Redemption price, percentage																100.00%
Carrying amount of long-term debt												$ 51,304,000				$ 51,304,000		203,545,000
5 1/2% Senior Subordinated Notes due 2022
Long Term Debt (Textuals) [Abstract]
Debt repurchases, face amount												$ 25,300,000		$ 11,000,000.0		$ 25,300,000
Amount of debt exchanged			219,900,000			94,200,000	364,000,000.0
Face value of notes	$ 1,250,000,000
Selling price of debt instrument	100.00%
Stated interest rate percentage												5.50%				5.50%
Carrying amount of long-term debt												$ 58,426,000				$ 58,426,000		314,662,000
4 5/8% Senior Subordinated Notes due 2023
Long Term Debt (Textuals) [Abstract]
Debt repurchases, face amount												$ 75,700,000				$ 75,700,000
Amount of debt exchanged			96,300,000			68,500,000	$ 245,800,000
Face value of notes									$ 1,200,000,000
Selling price of debt instrument									100.00%
Stated interest rate percentage												4.625%				4.625%
Carrying amount of long-term debt												$ 135,960,000				$ 135,960,000		$ 307,978,000
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]
Redemption price, percentage																104.50%
Debt Instrument, Redemption, Period One | 9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																109.25%
Debt Instrument, Redemption, Period One | 7 3/4% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																103.875%
Debt Instrument, Redemption, Period One | 7 1/2% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																103.75%
Debt Instrument, Redemption, Period One | 5 1/2% Senior Subordinated Notes due 2022
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																101.375%
Debt Instrument, Redemption, Period One | 4 5/8% Senior Subordinated Notes due 2023
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																100.771%
Debt Instrument, Redemption, Period Two | 9% Senior Secured Second Lien Notes due 2021
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																100.00%
Debt Instrument, Redemption, Period Two | 9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																104.625%
Debt Instrument, Redemption, Period Two | 5 1/2% Senior Subordinated Notes due 2022
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																100.00%
Debt Instrument, Redemption, Period Two | 4 5/8% Senior Subordinated Notes due 2023
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																100.00%
Debt Instrument, Redemption, Period Three | 9 1/4% Senior Secured Second Lien Notes due 2022
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																100.00%
Initial Redemption Period With Proceeds From Equity Offering Member | 7 3/4% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Redemption price, percentage																107.75%
Percentage of debt principal 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]
Redemption price, percentage																107.50%
Percentage of debt principal available to be redeemed																35.00%
Initial Redemption Period with Make-Whole Premium | 7 3/4% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
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]
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%
Senior Secured Bank Credit Facility | Letter of Credit
Senior Secured Bank Credit Facility [Abstract]
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases												100,000,000				$ 100,000,000
Senior Secured Bank Credit Facility | Swingline Loan
Senior Secured Bank Credit Facility [Abstract]
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases												$ 25,000,000				$ 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
Convertible Debt
Long Term Debt (Textuals) [Abstract]
Maximum total debt to EBITDA requirement																2.5
Senior Subordinated Notes
Long Term Debt (Textuals) [Abstract]
Amount of debt exchanged			468,400,000			$ 174,300,000
Maximum total debt to EBITDA requirement																2.5
Notes Repurchases
Long Term Debt (Textuals) [Abstract]
Gain on extinguishment of debt																$ 55,500,000
Portion Of Exchange Related To Senior Secured Notes
Long Term Debt (Textuals) [Abstract]
Gain on extinguishment of debt			0
Portion Of Exchange Related To Senior Secured Notes | 7 3/4% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Face value of notes		3,800,000	425,400,000
Unamortized debt issuance costs			6,900,000
Portion Of Exchange Related To Senior Secured Notes | 7 1/2% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Amount of debt exchanged		$ 4,000,000.0	425,400,000
Notes Exchange
Long Term Debt (Textuals) [Abstract]
Gain on extinguishment of debt																$ 100,500,000
Notes Exchange | 7 3/4% Senior Secured Second Lien Notes due 2024
Long Term Debt (Textuals) [Abstract]
Face value of notes			$ 102,600,000

[1] Consists of discounts related to the issuance during June 2019 of our new 7¾% Senior Secured Second Lien Notes due 2024 (the “7¾% Senior Secured Notes”) and new 6⅜% Convertible Senior Notes due 2024 (the “2024 Convertible Senior Notes”) of $27.0 million and $74.8 million, respectively (see 2019 Debt Reduction Transactions below) as of December 31, 2019.