Long-Term Debt - Other Long-Term Debt (Details) - Wells Fargo Bank N.A. - Line of credit
$ in Millions
 12 Months Ended
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Aug. 01, 2016
USD ($)
Oct. 08, 2015
USD ($)
Feb. 23, 2015
USD ($)
Revolving credit facility | Revolver            
Other Long-Term Debt            
Borrowing base       $ 425.0 $ 510.0 $ 562.5
Cash balance threshold       $ 30.0    
Average interest rate (as a percent) 2.40% 2.39%        
Average outstanding balance $ 172.3 $ 144.9        
Total interest and commitment fees $ 5.3 $ 5.1 $ 9.5      
Covenant, total leverage ratio 4.0          
Covenant, current ratio 1.0          
Total leverage ratio 3.9          
Current ratio 3.5          
Revolving credit facility | London Interbank Offered Rate (LIBOR) | Minimum | Revolver            
Other Long-Term Debt            
Margin interest rate (as a percent) 1.50%          
Revolving credit facility | London Interbank Offered Rate (LIBOR) | Maximum | Revolver            
Other Long-Term Debt            
Margin interest rate (as a percent) 2.50%          
Revolving credit facility | Federal Funds Effective Swap Rate | Revolver            
Other Long-Term Debt            
Margin interest rate (as a percent) 0.50%          
Revolving credit facility | One Month Adjust LIBO Rate | Revolver            
Other Long-Term Debt            
Margin interest rate (as a percent) 1.00%          
Revolving credit facility | Base rate | Minimum | Revolver            
Other Long-Term Debt            
Margin interest rate (as a percent) 0.50%          
Revolving credit facility | Base rate | Maximum | Revolver            
Other Long-Term Debt            
Margin interest rate (as a percent) 1.50%          
Term loan | Term Loan            
Other Long-Term Debt            
Total interest and commitment fees     $ 3.6