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Stock-Based Compensation - Narrative (Details)
1 Months Ended 12 Months Ended
Feb. 22, 2016
USD ($)
shares
Feb. 19, 2016
performance_criteria
Jan. 05, 2016
USD ($)
shares
Jan. 31, 2018
USD ($)
Feb. 28, 2015
Dec. 31, 2017
USD ($)
Award_Type
shares
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share-based compensation expense           $ 34,000,000 $ 26,000,000 $ 13,700,000
Excess tax expense for stock-based compensation           3,000,000    
Stock-based compensation tax benefit             2,126,000  
Stock-based compensation tax benefit               0
Defined contribution cost recognized           $ 2,600,000    
Deferred Compensation, Share-based Payments                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Common shares held in employee trust earned but not distributed (in shares) | shares           495,774    
Shares issued in period (in shares) | shares           0    
Restricted Stock Awards                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share-based compensation expense           $ 500,000 400,000 400,000
Award vesting period           3 years    
Compensation cost not yet recognized           $ 4,000,000    
Fair value of award           $ 900,000 200,000 200,000
Period of recognition for unrecognized compensation costs           2 years    
Aggregate intrinsic value           $ 4,600,000    
Weighted-average remaining contractual term of non-vested shares           1 year 4 months 18 days    
Restricted Stock Awards | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Expected forfeiture rate           5.00%    
Restricted Stock Awards | Graduated or graded vesting | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting period           3 years    
Restricted Stock Awards | Graduated or graded vesting | Maximum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting period           4 years    
Restricted Stock Units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share-based compensation expense           $ 1,400,000 1,400,000 1,400,000
Aggregate intrinsic value           $ 11,700,000    
Stock Appreciation Rights                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Term of award           7 years    
Aggregate intrinsic value           $ 600,000    
Weighted-average remaining contractual term of non-vested shares           1 year 1 month    
Stock Appreciation Rights | Graduated or graded vesting                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting period           3 years    
Award vesting percentage           33.33%    
Performance Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share-based compensation expense           $ 29,100,000 21,300,000 18,300,000
Award vesting period           3 years    
Compensation cost not yet recognized           $ 20,700,000    
Number of performance award types | Award_Type           3    
Period of recognition for unrecognized compensation costs           11 months 4 days    
Aggregate intrinsic value           $ 79,500,000    
Weighted-average remaining contractual term of non-vested shares           1 year 1 month 25 days    
Number of performance awards where the performance period has ended | Award_Type           2    
Performance Shares | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Expected forfeiture rate           0.00%    
Performance Shares | Maximum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Expected forfeiture rate           5.00%    
Internal Metrics Performance Share Awards                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of performance award types | Award_Type           2    
Rights to share portion of award, maximum percent           100.00%    
Market Based Performance Share Awards                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of performance award types | Award_Type           1    
Rights to share portion of award, maximum percent           100.00%    
Rights to cash portion of award, maximum percent           100.00%    
Employee Performance Share Awards                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting period         3 years 3 years    
Number of performance criteria | performance_criteria   3            
Number of performance awards issued and certified (in shares) | shares 317,790              
Grant date fair value of performance shares issued and certified $ 8,800,000              
Employee Performance Share Awards | Performance metric: average production                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting percentage           33.33%    
Employee Performance Share Awards | Performance metric: average finding costs                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting percentage           33.33%    
Employee Performance Share Awards | Performance metric: average reserve replacement                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting percentage           33.33%    
Hybrid Performance Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Minimum operating cash flow for performance based award           $ 100,000,000    
Hybrid Performance Shares | Graduated or graded vesting                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting period           3 years    
Hybrid Performance Shares | 25% vesting on first and second anniversary                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting percentage           25.00%    
Hybrid Performance Shares | 50% vesting on third anniversary                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting percentage           50.00%    
TSR Performance Share Awards                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Performance period of peer group           3 years    
Cash payments for share-based compensation           $ 0 1,800,000 $ 7,000,000
Number of performance awards issued and certified (in shares) | shares     292,421          
Grant date fair value of performance shares issued and certified     $ 5,600,000          
TSR Performance Share Awards | Liability                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Current portion of share-based liability           3,300,000 0  
Noncurrent portion of share-based liability           6,600,000 $ 2,100,000  
SEIP                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share-based compensation expense           $ 0    
Percent of aggregate distribution paid immediately           25.00%    
Percent of aggregate distribution paid subsequently           75.00%    
Subsequent Event | TSR Performance Share Awards                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Payments for stock-based compensation       $ 3,300,000