Subsequent Events (Details) - USD ($)
Jan. 14, 2019
Dec. 31, 2018
Aug. 18, 2016
May 20, 2014
Subsequent Event [Line Items]        
Outstanding balance   $ 2,084,302,000    
Unsecured Debt        
Subsequent Event [Line Items]        
Outstanding balance   300,000,000    
Stated rate     4.45%  
Convertible Notes        
Subsequent Event [Line Items]        
Outstanding balance   $ 747,500,000    
Convertible Senior Notes Due 2019 | Convertible Notes        
Subsequent Event [Line Items]        
Stated rate       2.875%
Revolving Credit Facility | Credit Facility 2019 | Unsecured Debt | Subsequent Event        
Subsequent Event [Line Items]        
Maximum borrowing capacity $ 800,000,000.0      
Facility fee percentage 0.25%      
Increased borrowing capacity under accordion feature $ 400,000,000      
Term Loan | A-1 Term Loan | Unsecured Debt | Subsequent Event        
Subsequent Event [Line Items]        
Maximum borrowing capacity 420,000,000.0      
Increased borrowing capacity under accordion feature 200,000,000      
Term Loan | A-2 Term Loan | Unsecured Debt | Subsequent Event        
Subsequent Event [Line Items]        
Maximum borrowing capacity $ 400,000,000.0      
Ticking fee percentage 0.20%      
Outstanding balance $ 0      
Increased borrowing capacity under accordion feature $ 200,000,000      
LIBOR | Revolving Credit Facility | Credit Facility 2019 | Unsecured Debt | Subsequent Event        
Subsequent Event [Line Items]        
Basis spread on variable rate 1.10%      
LIBOR | Term Loan | A-1 Term Loan | Unsecured Debt | Subsequent Event        
Subsequent Event [Line Items]        
Basis spread on variable rate 1.25%      
LIBOR | Term Loan | A-2 Term Loan | Unsecured Debt | Subsequent Event        
Subsequent Event [Line Items]        
Basis spread on variable rate 1.25%