Debt - Term Loans - Narrative (Details) - USD ($)
3 Months Ended 4 Months Ended 5 Months Ended 9 Months Ended
Sep. 16, 2019
Jan. 14, 2019
Sep. 30, 2019
Apr. 30, 2019
Sep. 30, 2019
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Debt Instrument [Line Items]                
Unamortized deferred financing costs     $ 18,569,000   $ 18,569,000 $ 18,569,000   $ 14,932,000
(Loss) gain on debt extinguishment     $ (5,580,000)     $ (11,473,000) $ 27,092,000  
Convertible Senior Notes Due 2019 | Convertible Senior Notes                
Debt Instrument [Line Items]                
Stated interest rate     2.875%   2.875% 2.875%    
Term loans | 2015 Term Loan | Unsecured Debt                
Debt Instrument [Line Items]                
Maximum borrowing capacity               420,000,000.0
Unamortized deferred financing costs               $ 400,000
Term loans | A-1 Term Loan | Unsecured Debt                
Debt Instrument [Line Items]                
Maximum borrowing capacity   $ 420,000,000.0            
Increased borrowing capacity under accordion feature   $ 200,000,000.0            
Credit facility maturity date   Mar. 31, 2024            
Term loans | A-1 Term Loan | Unsecured Debt | LIBOR                
Debt Instrument [Line Items]                
Basis spread on variable rate       1.25% 1.00%      
Term loans | A-2 Term Loan | Unsecured Debt                
Debt Instrument [Line Items]                
Maximum borrowing capacity   $ 400,000,000.0            
Increased borrowing capacity under accordion feature   $ 200,000,000.0            
Ticking fee percentage   0.20%            
Term loans | A-2 Term Loan | Unsecured Debt | LIBOR                
Debt Instrument [Line Items]                
Basis spread on variable rate         1.00%      
Term loans | A-1 Term Loans and A-2 Term Loans | Unsecured Debt                
Debt Instrument [Line Items]                
(Loss) gain on debt extinguishment $ 5,300,000