Quarterly report pursuant to Section 13 or 15(d)

LONG-TERM DEBT (Narrative) (Details)

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LONG-TERM DEBT (Narrative) (Details)
1 Months Ended 3 Months Ended 9 Months Ended
May 21, 2018
USD ($)
Nov. 21, 2017
May 04, 2017
USD ($)
bank
Dec. 21, 2016
USD ($)
Oct. 14, 2016
USD ($)
Jan. 31, 2016
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Oct. 11, 2017
USD ($)
May 05, 2017
USD ($)
Mar. 29, 2017
USD ($)
Jun. 04, 2015
USD ($)
Apr. 21, 2015
USD ($)
Debt Instrument [Line Items]                                
Capitalized interest expense, undeveloped properties             $ 1,600,000 $ 2,100,000 $ 4,000,000 $ 8,800,000            
Debt issuance costs, net             31,824,000   31,824,000   $ 34,781,000          
Construction loan                                
Debt Instrument [Line Items]                                
Debt issuance costs, net             $ 100,000   $ 100,000              
Revolving credit agreement | Maximum                                
Debt Instrument [Line Items]                                
Debt covenant ratio for future EBITDAX             4.00   4.00              
Revolving credit agreement | Revolving credit agreement                                
Debt Instrument [Line Items]                                
Debt covenant ratio for EBITDAX             3.00   3.00              
6.000% senior unsecured notes due 2024 | Senior notes                                
Debt Instrument [Line Items]                                
Long-term debt             $ 650,000,000   $ 650,000,000   650,000,000          
Stated interest rate, percent         6.00%   6.00%   6.00%              
Debt instrument, amount         $ 650,000,000.0                      
Proceeds from issuance of Senior Notes         $ 638,900,000                      
Debt issuance costs, net             $ 9,000,000   $ 9,000,000              
6.625% senior unsecured notes due 2023 | Senior notes                                
Debt Instrument [Line Items]                                
Long-term debt             $ 350,000,000   $ 350,000,000   350,000,000          
Stated interest rate, percent             6.625%   6.625%             6.625%
Debt instrument, amount                               $ 350,000,000.0
Long term debt, net of initial purchaser discounts and commissions and estimated offering expenses                               $ 343,600,000
Debt issuance costs, net             $ 4,600,000   $ 4,600,000              
6.375% senior unsecured notes due 2025 | Senior notes                                
Debt Instrument [Line Items]                                
Long-term debt             $ 600,000,000   $ 600,000,000   600,000,000          
Stated interest rate, percent       6.375%     6.375%   6.375%              
Debt instrument, amount       $ 600,000,000.0                        
Proceeds from issuance of Senior Notes       $ 584,700,000                        
Debt issuance costs, net             $ 12,900,000   $ 12,900,000              
6.375% senior unsecured notes due 2026 | Senior notes                                
Debt Instrument [Line Items]                                
Long-term debt             $ 450,000,000   $ 450,000,000   450,000,000          
Stated interest rate, percent             6.375%   6.375%     6.375%        
Debt instrument, amount                       $ 450,000,000.0        
Long term debt, net of initial purchaser discounts and commissions and estimated offering expenses                       $ 444,100,000        
Debt issuance costs, net             $ 5,200,000   $ 5,200,000              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement                                
Debt Instrument [Line Items]                                
Credit facility interest rate at the eurodollar rate                 3.72%              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Base rate | Minimum                                
Debt Instrument [Line Items]                                
Stated interest rate, percent             0.25%   0.25%              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Base rate | Maximum                                
Debt Instrument [Line Items]                                
Stated interest rate, percent             1.25%   1.25%              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Federal funds rate                                
Debt Instrument [Line Items]                                
Basis spread, percent                 0.50%              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Eurodollar rate                                
Debt Instrument [Line Items]                                
Basis spread, percent                 1.00%              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Eurodollar rate | Minimum                                
Debt Instrument [Line Items]                                
Stated interest rate, percent             1.25%   1.25%              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Eurodollar rate | Maximum                                
Debt Instrument [Line Items]                                
Stated interest rate, percent             2.25%   2.25%              
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Revolving credit agreement                                
Debt Instrument [Line Items]                                
Long-term debt             $ 60,000,000   $ 60,000,000   0          
Maximum borrowing capacity             1,500,000,000.0   1,500,000,000.0              
Minimum acquisition payment limit                           $ 50,000,000    
Minimum disposition of property limit                           $ 50,000,000    
Borrowing base $ 1,400,000,000   $ 700,000,000       1,200,000,000   1,200,000,000       $ 1,000,000,000      
Number of banks added to syndicate (in banks) | bank     5                          
Increase (decrease) in interest rate 0.25% 0.50%                            
Remaining borrowing capacity             623,800,000   623,800,000              
Nova Scotia, Amegy, KeyBank | Letter of credit | Revolving credit agreement                                
Debt Instrument [Line Items]                                
Line of credit facility, elected commitment $ 1,000,000,000.0           1,000,000,000.0   1,000,000,000.0              
Credit facility outstanding             316,200,000   316,200,000              
Disposition costs, maximum expenses allowed                 3,000,000.0              
InterBank | Revolving credit agreement | Construction loan                                
Debt Instrument [Line Items]                                
Maximum borrowing capacity                             $ 24,500,000.0  
Stated interest rate, percent                             4.50%  
InterBank | Letter of credit | Construction loan                                
Debt Instrument [Line Items]                                
Long-term debt             $ 23,296,000   $ 23,296,000   $ 23,724,000          
Required minimum down payment, percent           30.00%