v3.8.0.1
Debt and Credit Agreements - Narrative (Details)
1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2015
fiscal_period
Apr. 17, 2015
May 31, 2016
USD ($)
Sep. 30, 2014
USD ($)
Investor
Tranche
Dec. 31, 2010
USD ($)
Investor
Tranche
Dec. 31, 2008
USD ($)
Investor
Jul. 31, 2008
USD ($)
Investor
Tranche
Jun. 30, 2016
USD ($)
Dec. 31, 2017
USD ($)
fiscal_period
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 19, 2017
USD ($)
Apr. 19, 2016
USD ($)
Debt Instrument [Line Items]                          
2018                 $ 304,000,000        
2020                 87,000,000        
2021                 188,000,000        
Repayments of debt                 0 $ 587,000,000 $ 604,000,000    
Loss on repurchase of debt                 0 4,709,000 $ 0    
Deferred financing costs capitalized                 $ 6,109,000 $ 7,470,000      
6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Weighted-average interest rate (as a percent)                 6.51% 6.51%      
Long-term debt including unamortized debt issuance costs                 $ 361,000,000 $ 361,000,000      
9.78% senior notes                          
Debt Instrument [Line Items]                          
Interest rate (as a percent)                 9.78% 9.78%      
Long-term debt including unamortized debt issuance costs                 $ 67,000,000 $ 67,000,000      
5.58% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Weighted-average interest rate (as a percent)                 5.58% 5.58%      
Long-term debt including unamortized debt issuance costs                 $ 175,000,000 $ 175,000,000      
3.65% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Weighted-average interest rate (as a percent)                 3.65% 3.65%      
Long-term debt including unamortized debt issuance costs                 $ 925,000,000 $ 925,000,000      
Revolving credit facility                          
Debt Instrument [Line Items]                          
Remaining borrowing capacity on line of credit                 $ 1,700,000,000        
Fiscal quarters for reduction in coverage ratio | fiscal_period                 4        
Minimum required annual coverage ratio                 2.8        
Maximum borrowing capacity on line of credit                         $ 3,200,000,000.0
Minimum current ratio                 1.0        
Long-term debt including unamortized debt issuance costs                 $ 0 $ 0      
Interest rate during period                   2.30% 2.20%    
Senior Notes                          
Debt Instrument [Line Items]                          
Fiscal quarters for reduction in coverage ratio | fiscal_period                 4        
Minimum required annual coverage ratio                 2.8        
Deferred financing costs capitalized                 $ 1,900,000        
Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal             $ 425,000,000            
Number of institutional investors | Investor             41            
Number of debt tranches | Tranche             3            
Senior Notes | 9.78% senior notes                          
Debt Instrument [Line Items]                          
Principal           $ 67,000,000              
Number of institutional investors | Investor           4              
Term           10 years              
Interest rate (as a percent)           9.78%              
Senior Notes | 5.58% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal         $ 175,000,000                
Number of institutional investors | Investor         8                
Number of debt tranches | Tranche         3                
Senior Notes | 3.65% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal       $ 925,000,000                  
Number of institutional investors | Investor       24                  
Number of debt tranches | Tranche       3                  
Minimum | Revolving credit facility                          
Debt Instrument [Line Items]                          
Unused capacity fee percentage   0.30%                      
Maximum | Revolving credit facility                          
Debt Instrument [Line Items]                          
Unused capacity fee percentage   0.50%                      
December 31, 2017 | Senior Notes                          
Debt Instrument [Line Items]                          
Minimum required asset coverage ratio 1.25                        
March 31, 2018 | Senior Notes                          
Debt Instrument [Line Items]                          
Minimum required asset coverage ratio 1.75                        
Maintain coverage ratio for 2 consecutive quarters or receive investment grade rating from Standard and Poors or Moody's | Senior Notes                          
Debt Instrument [Line Items]                          
Maximum leverage coverage ratio 3.0               3.0        
Fiscal quarters for reduction in coverage ratio | fiscal_period 2                        
Increase in rate based upon coverage and leverage ratio | Senior Notes                          
Debt Instrument [Line Items]                          
Basis spread on variable rate                 0.00%        
Increase in rate based upon coverage and leverage ratio | Minimum | Senior Notes                          
Debt Instrument [Line Items]                          
Basis spread on variable rate                 0.00%        
Increase in rate based upon coverage and leverage ratio | Maximum | Senior Notes                          
Debt Instrument [Line Items]                          
Basis spread on variable rate                 1.25%        
Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Amount of principal repurchased     $ 64,000,000                    
Repayments of debt     68,300,000                    
Loss on repurchase of debt               $ 4,700,000          
Tranche 1 | Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal             $ 245,000,000            
Term             10 years            
Interest rate (as a percent)             6.44%            
Tranche 1 | Senior Notes | 5.58% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal         $ 88,000,000                
Term         10 years                
Interest rate (as a percent)         5.42%                
Tranche 1 | Senior Notes | 3.65% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal       $ 100,000,000                  
Term       7 years                  
Interest rate (as a percent)       3.24%                  
Tranche 1 | Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Amount of principal repurchased     8,000,000                    
Tranche 2 | Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal             $ 100,000,000            
Term             12 years            
Interest rate (as a percent)             6.54%            
Tranche 2 | Senior Notes | 5.58% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal         $ 25,000,000                
Term         12 years                
Interest rate (as a percent)         5.59%                
Tranche 2 | Senior Notes | 3.65% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal       $ 575,000,000                  
Term       10 years                  
Interest rate (as a percent)       3.67%                  
Tranche 2 | Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Amount of principal repurchased     13,000,000                    
Tranche 3 | Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal             $ 80,000,000            
Term             15 years            
Interest rate (as a percent)             6.69%            
Tranche 3 | Senior Notes | 5.58% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal         $ 62,000,000                
Term         15 years                
Interest rate (as a percent)         5.80%                
Tranche 3 | Senior Notes | 3.65% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Principal       $ 250,000,000                  
Term       12 years                  
Interest rate (as a percent)       3.77%                  
Tranche 3 | Senior Notes | 6.51% weighted-average senior notes                          
Debt Instrument [Line Items]                          
Amount of principal repurchased     $ 43,000,000                    
LIBOR | Minimum | Revolving credit facility                          
Debt Instrument [Line Items]                          
Basis spread on variable rate                 0.50%        
LIBOR | Maximum | Revolving credit facility                          
Debt Instrument [Line Items]                          
Basis spread on variable rate                 3.00%        
LIBOR | Maintain coverage ratio for 2 consecutive quarters or receive investment grade rating from Standard and Poors or Moody's | Minimum | Revolving credit facility                          
Debt Instrument [Line Items]                          
Basis spread on variable rate                 0.50%        
LIBOR | Maintain coverage ratio for 2 consecutive quarters or receive investment grade rating from Standard and Poors or Moody's | Maximum | Revolving credit facility                          
Debt Instrument [Line Items]                          
Basis spread on variable rate                 2.25%        
Assets Held-for-sale                          
Debt Instrument [Line Items]                          
Consideration                 $ 762,195,000        
Assets Held-for-sale | Eagle Ford                          
Debt Instrument [Line Items]                          
Consideration                       $ 765,000,000