Long-Term Debt (Details)
May 04, 2018
Nov. 30, 2017
USD ($)
Dec. 28, 2016
redetermination
Jun. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
Revolving Credit Facility | Line of Credit          
Debt Instrument [Line Items]          
Borrowing base       $ 800,000,000  
Elected commitments       600,000,000  
Line of credit, term 5 years        
Borrowings, outstanding amount       30,000,000  
Remaining borrowing capacity, net of current borrowings outstanding       569,100,000  
Maximum borrowing base       1,500,000,000  
Number of optional borrowing base redeterminations | redetermination     2    
Letter of Credit | Line of Credit          
Debt Instrument [Line Items]          
Letters of credit outstanding       900,000  
Minimum | Revolving Credit Facility | Line of Credit          
Debt Instrument [Line Items]          
Debt instrument, covenant, minimum current ratio     1    
Maximum | Revolving Credit Facility | Line of Credit          
Debt Instrument [Line Items]          
Debt instrument, covenant, maximum leverage ratio     4    
Senior Notes Due 2026 | Senior Notes          
Debt Instrument [Line Items]          
Long-term debt   $ 400,000,000      
Interest rate, stated percentage   5.375%      
Proceeds from borrowings, net of issuance costs   $ 391,000,000      
Debt issuance costs   $ 9,000,000      
Percentage of principal amount, eligible to be redeemed   35.00%      
Percentage of principal amount, redeemable   65.00%      
Percentage of principal amount, change in control   101.00%      
Percentage of principal amount, event of default   25.00%      
Debt issuance costs netted to Senior Notes       $ 8,800,000 $ 9,200,000
Debt Instrument, Redemption, Period One | Senior Notes Due 2026 | Senior Notes          
Debt Instrument [Line Items]          
Redemption price percentage   105.375%      
Debt Instrument, Redemption, Period Two | Senior Notes Due 2026 | Senior Notes          
Debt Instrument [Line Items]          
Redemption price percentage   102.688%      
Debt Instrument, Redemption, Period Three | Senior Notes Due 2026 | Senior Notes          
Debt Instrument [Line Items]          
Redemption price percentage   101.344%      
Debt Instrument, Redemption, Period Four | Senior Notes Due 2026 | Senior Notes          
Debt Instrument [Line Items]          
Redemption price percentage   100.00%