Debt - Revolving Credit Facilities - Narrative (Details) - USD ($)
 9 Months Ended
Mar. 31, 2015
Sep. 30, 2017
Dec. 31, 2016
Aug. 18, 2016
Apr. 27, 2016
Line of Credit Facility [Line Items]          
Total debt, gross   $ 3,937,485,000 $ 3,754,633,000    
Unsecured Debt          
Line of Credit Facility [Line Items]          
Line of credit facility, maximum borrowing capacity $ 600,000,000       $ 800,000,000
Line of credit facility, accordion feature, increase limit $ 1,000,000,000        
Commitment fee (as a percent)   0.25%      
Origination costs   $ 4,800,000   $ 3,400,000  
Letters of credit issued   0      
Line of credit facility, remaining borrowing capacity   $ 414,000,000      
Unsecured Debt | Minimum          
Line of Credit Facility [Line Items]          
Commitment fee (as a percent) 0.125%        
Unsecured Debt | Maximum          
Line of Credit Facility [Line Items]          
Commitment fee (as a percent) 0.30%        
Unsecured Debt | LIBOR          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (as a percent)   1.25%      
Unsecured Debt | LIBOR | Minimum          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (as a percent) 0.875%        
Unsecured Debt | LIBOR | Maximum          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (as a percent) 1.55%        
Unsecured Debt | Base Rate | Minimum          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (as a percent) 0.00%        
Unsecured Debt | Base Rate | Maximum          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (as a percent) 0.55%        
Unsecured Debt | Swing-line Loans          
Line of Credit Facility [Line Items]          
Line of credit facility, maximum borrowing capacity $ 50,000,000        
Unsecured Debt | Letters of Credit          
Line of Credit Facility [Line Items]          
Line of credit facility, maximum borrowing capacity $ 60,000,000        
Revolving Credit Facility          
Line of Credit Facility [Line Items]          
Total debt, gross   $ 386,000,000      
Deferred Costs And Other Assets | Revolving Credit Facility          
Line of Credit Facility [Line Items]          
Unamortized deferred financing costs   $ 2,000,000 $ 2,900,000