FRESH START ACCOUNTING - Additional Information (Details) - USD ($)			1 Months Ended		2 Months Ended	3 Months Ended
	Feb. 28, 2017	Feb. 27, 2017	Mar. 31, 2017	Oct. 31, 2016	Feb. 28, 2017	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fresh-Start Adjustment [Line Items]
Accumulated deficit	$ 554,737,000				$ 554,737,000	$ 326,073,000	$ 308,168,000
Enterprise value	$ 419,720,000				419,720,000
Annual escalation adjustment rate	2.00%
Expected period for development to begin	5 years
Proved reserves	$ 380,800,000				380,800,000
Probable and possible reserves	16,800,000				16,800,000
Unevaluated properties reserves	80,200,000				80,200,000
Fair value of asset retirement obligations	$ 290,067,000				290,067,000
Credit-adjusted risk free rate	12.00%
Repayment of outstanding borrowings under Pre-Emergence Credit Agreement	$ 341,500,000		$ 0			$ 0
New shares issued in reorganization (in shares)	20,000,000					682
Emergence and success fees	$ 15,200,000
Professional fees	2,700,000
Predecessor
Fresh-Start Adjustment [Line Items]
Accumulated deficit	(3,610,000)				(3,610,000)			$ (637,282,000)
Repayment of outstanding borrowings under Pre-Emergence Credit Agreement					$ 341,500,000
New shares issued in reorganization (in shares)			0		47,390
Emergence and success fees					$ 10,600,000
Professional fees					8,900,000
Appalachia Properties | Disposal Group, Disposed of by Sale
Fresh-Start Adjustment [Line Items]
Indemnity escrow release		$ 10,000,000
Revaluation of Assets
Fresh-Start Adjustment [Line Items]
Write off of unamortized debt issuance costs	2,600,000
Revaluation of Assets | Tug Hill, Inc
Fresh-Start Adjustment [Line Items]
Net reimbursement in connection with the sale of asset	700,000				700,000
Loss on contract termination				$ 1,800,000
Revaluation of Liabilities | Senior Notes | 7 ½% Senior Notes due 2022
Fresh-Start Adjustment [Line Items]
Aggregate principal amount of senior subordinated notes	225,000,000				225,000,000
Revaluation of Liabilities | Predecessor
Fresh-Start Adjustment [Line Items]
Repayment of outstanding borrowings under Pre-Emergence Credit Agreement					341,500,000
Revaluation of Liabilities | Leasing Arrangement
Fresh-Start Adjustment [Line Items]
Loss on contract termination	400,000
Revaluation of Liabilities | Appalachia Properties | Disposal Group, Disposed of by Sale
Fresh-Start Adjustment [Line Items]
Settlement of a property tax accrual	2,600,000				$ 2,600,000
Revaluation of Liabilities | Deferred Bonus | 2016 Incentive Plan
Fresh-Start Adjustment [Line Items]
Deferred compensation arrangement compensation expense	$ 2,000,000
Exchange of Stock for Stock
Fresh-Start Adjustment [Line Items]
Estimated fair value of the warrants (in usd per share)	$ 4.43				$ 4.43
Exchange of Stock for Stock | Predecessor Company's Common Stockholders
Fresh-Start Adjustment [Line Items]
Warrants issued in reorganization (in shares)	3,500,000
Exercise price of warrants or rights (in usd per share)	$ 42.04				$ 42.04
Exercise period for warrants	4 years
Exchange of Stock for Stock | Senior Notes | 7 ½% Senior Notes due 2022 | Predecessor Company's Noteholders
Fresh-Start Adjustment [Line Items]
New shares issued in reorganization (in shares)	1,000,000
Exchange of Stock for Stock | Convertible Debt | 1 ¾% Senior Convertible Notes due 2017 | Predecessor Company's Noteholders
Fresh-Start Adjustment [Line Items]
New shares issued in reorganization (in shares)	19,000,000
Income Approach Valuation Technique
Fresh-Start Adjustment [Line Items]
Discounted weighted average cost of capital rate	12.50%
Minimum
Fresh-Start Adjustment [Line Items]
Enterprise value	$ 300,000,000				$ 300,000,000
Maximum
Fresh-Start Adjustment [Line Items]
Enterprise value	450,000,000				450,000,000
Accumulated Deficit
Fresh-Start Adjustment [Line Items]
Accumulated deficit	0				0	$ (230,067,000)	$ (247,639,000)
Accumulated Deficit | Predecessor
Fresh-Start Adjustment [Line Items]
Accumulated deficit	$ (1,665,892,000)				$ (1,665,892,000)			$ (2,296,209,000)