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Debt - Senior Notes (Details) - USD ($)
3 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Apr. 12, 2017
Oct. 18, 2016
May 24, 2016
Apr. 04, 2016
Sep. 24, 2015
Debt Instrument [Line Items]                  
Loss on extinguishment of debt   $ 0 $ 0 $ 47,200,000          
2026 Senior Notes                  
Debt Instrument [Line Items]                  
Senior notes, noncurrent   $ 600,000,000.0 $ 600,000,000       $ 600,000,000.0    
Stated percentage   5.50% 5.50%       5.50%    
Percentage of principal amount that may be redeemed   105.50%              
Minimum percentage of notes not eligible for early redemption   65.00%              
Senior notes, percent exchanged           100.00%      
Deferred financing costs       $ 3,100,000          
Debt instrument amortization period deferred financing costs (in years       10 years          
Loss on extinguishment of debt       $ 5,900,000          
2026 Senior Notes | Any time on or after June 15, 2021                  
Debt Instrument [Line Items]                  
Redemption price, percentage   102.75%              
2026 Senior Notes | Beginning on June 15, 2024                  
Debt Instrument [Line Items]                  
Redemption price, percentage   100.00%              
2026 Senior Notes | Any time prior to June 15, 2021 with a 'make-whole' premium and accrued and unpaid interest, if any                  
Debt Instrument [Line Items]                  
Percentage of redemption on notes   100.00%              
2026 Senior Notes | Any time prior to June 15, 2019 with the net cash proceeds from certain equity offerings plus accrued and unpaid interest, if any                  
Debt Instrument [Line Items]                  
Percentage of redemption on notes   35.00%              
Securitized debt                  
Debt Instrument [Line Items]                  
Senior notes, noncurrent   $ 375,000,000.0 $ 375,000,000            
Stated percentage   6.875%              
Loss on extinguishment of debt       $ 23,600,000          
Write-off of deferred financing costs $ 4,800,000                
2023 Senior Notes                  
Debt Instrument [Line Items]                  
Senior notes, noncurrent   $ 450,000,000.0 $ 450,000,000           $ 450,000,000.0
Stated percentage   5.625% 5.625%           5.625%
Percentage of principal amount that may be redeemed   105.625%              
Minimum percentage of notes not eligible for early redemption   65.00%              
Senior notes, percent exchanged               100.00%  
2023 Senior Notes | Any time on or after October 15, 2018                  
Debt Instrument [Line Items]                  
Redemption price, percentage   104.219%              
2023 Senior Notes | Beginning on October 15, 2021                  
Debt Instrument [Line Items]                  
Redemption price, percentage   100.00%              
2023 Senior Notes | Any time prior to October 15, 2018 with a 'make-whole' premium and accrued and unpaid interest, if any                  
Debt Instrument [Line Items]                  
Percentage of redemption on notes   100.00%              
2023 Senior Notes | Any time prior to October 15, 2018 with the net cash proceeds from certain equity offerings plus accrued and unpaid interest, if any                  
Debt Instrument [Line Items]                  
Redemption price, percentage   35.00%              
Revolver                  
Debt Instrument [Line Items]                  
Principal borrowing capacity, maximum         $ 120,000,000.0        
Significant Other Observable Inputs (Level 2) | 2026 Senior Notes                  
Debt Instrument [Line Items]                  
Notes, fair value   $ 549,300,000 $ 618,100,000            
Significant Other Observable Inputs (Level 2) | 2023 Senior Notes                  
Debt Instrument [Line Items]                  
Notes, fair value   $ 435,600,000 $ 470,900,000