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Mortgages and Notes Payable (Details)
3 Months Ended
Mar. 31, 2018
USD ($)
extensions
Apr. 17, 2018
USD ($)
Dec. 31, 2017
USD ($)
Debt Instrument [Line Items]      
Mortgages and notes payable $ 2,112,584,000   $ 2,014,333,000
Unamortized debt issuance costs (10,638,000)   (8,161,000)
Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Maximum borrowing capacity on revolving credit facility $ 600,000,000    
Maturity date on revolving credit facility Jan. 01, 2022    
Additional borrowing capacity on revolving credit facility $ 400,000,000    
Number of additional extensions | extensions 2    
Term of optional extension 6 months    
Annual facility fee (in hundredths) 0.20%    
Amount outstanding on revolving credit facility $ 0    
Outstanding letters of credit on revolving credit facility 500,000    
Unused borrowing capacity on revolving credit facility 599,500,000    
4.125% (4.271% effective rate) Notes due 2028 [Member]      
Debt Instrument [Line Items]      
Principal debt amount $ 350,000,000    
Interest rate (in hundredths) 4.125%    
Scheduled maturity date Mar. 15, 2028    
Original issue discount $ 4,100,000    
Effective interest rate (in hundredths) 4.271%    
Debt issuance costs incurred $ 2,900,000    
Secured indebtedness [Member]      
Debt Instrument [Line Items]      
Mortgages and notes payable 98,537,000   98,981,000
Aggregate undepreciated book value of secured real estate assets 147,600,000    
Unsecured indebtedness [Member]      
Debt Instrument [Line Items]      
Mortgages and notes payable $ 2,024,685,000   $ 1,923,513,000
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Facility interest rate basis LIBOR plus 100 basis points    
Interest rate, basis spread (in hundredths) 1.00%    
Subsequent Event [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Amount outstanding on revolving credit facility   $ 172,000,000  
Outstanding letters of credit on revolving credit facility   500,000  
Unused borrowing capacity on revolving credit facility   $ 427,500,000