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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
Feb. 28, 2015
Dec. 31, 2016
USD ($)
Award_Type
shares
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation expense         $ 26,000,000 $ 13,700,000 $ 21,500,000
Stock-based compensation tax benefit         2,126,000   1,375,000
Stock-based compensation tax benefit         0 0 (1,375,000)
Defined contribution cost recognized         $ 1,800,000 (6,400,000) (4,900,000)
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         38,400    
Restricted Stock Awards              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation expense         $ 400,000 400,000 1,000,000
Award vesting period         3 years    
Compensation cost not yet recognized         $ 100,000    
Fair value of award         200,000 200,000 600,000
Aggregate intrinsic value         $ 1,000,000    
Weighted-average remaining contractual term of non-vested shares         3 months 17 days    
Restricted Stock Awards | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected forfeiture rate         5.00%    
Restricted Stock Awards | Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected forfeiture rate         6.00%    
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 1,500,000
Aggregate intrinsic value         $ 8,100,000    
Stock Appreciation Rights              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation expense             100,000
Compensation cost not yet recognized             0
Term of award         7 years    
Aggregate intrinsic value         $ 5,000,000    
Weighted-average remaining contractual term of non-vested shares         1 year 5 months 21 days    
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         $ 21,300,000 18,300,000 20,800,000
Award vesting period         3 years    
Compensation cost not yet recognized         $ 19,300,000    
Number of performance award types | Award_Type         3    
Period of recognition for unrecognized compensation costs         11 months 4 days    
Aggregate intrinsic value         $ 55,100,000    
Weighted-average remaining contractual term of non-vested shares         1 year 3 months 14 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         6.00%    
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 225,780            
Grant date fair value of performance shares issued and certified $ 8,900,000            
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         $ 1,800,000 7,000,000 14,300,000
Number of performance awards issued and certified (in shares) | shares     157,147        
Grant date fair value of performance shares issued and certified     $ 5,000,000        
TSR Performance Share Awards | Liability              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Current portion of share-based liability         0 1,800,000  
Noncurrent portion of share-based liability         2,100,000 900,000  
SEIP              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation expense         $ 0 $ (300,000) 3,000,000
Number of trading days during which the closing price meets or exceeds the goal price         20 days    
Number of consecutive trading days for payout         60 days    
Period for interim goal         2 years    
Period for final goal         4 years    
Percent of employee salary for interim goal         20.00%    
Percent of employee salary for final goal         50.00%    
Percent of employee salary if interim goal is met         30.00%    
Payments related to share-based compensation             $ 13,000,000
Percent of aggregate distribution paid immediately         25.00%    
Percent of aggregate distribution paid subsequently         75.00%