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Borrowing Arrangements - Second Amendment Unsecured Credit Facility And Term Loan (Details)
12 Months Ended
Dec. 31, 2020
USD ($)
extension
Dec. 31, 2018
USD ($)
Rate
Dec. 31, 2019
USD ($)
Debt Instrument      
Line of credit facility, maximum borrowing capacity   $ 400,000,000.0  
Term loan, net $ 0   $ 198,949,000
Number of extension periods (extension) | extension 2    
Extension period (months) 6 months    
Commitment fee   3,700,000  
Repayments of debt   $ 196,800,000  
Debt Instrument, Interest Rate, Effective Percentage 3.05%    
Gain (Loss) on Extinguishment of Debt $ 9,000,000.0    
Unsecured line of credit     160,000,000
Minimum      
Debt Instrument      
Derivative interest rate, percent | Rate   0.15%  
Maximum      
Debt Instrument      
Derivative interest rate, percent | Rate   0.35%  
Line of Credit | Letter of Credit      
Debt Instrument      
Term loan, net 200,000,000.0    
Unsecured line of credit 222,000,000   $ 160,000,000.0
Line of credit remaining borrowing amount 178,000,000.0    
Line of Credit | LIBOR | Minimum      
Debt Instrument      
Variable rate, percent | Rate   1.10%  
Line of Credit | LIBOR | Maximum      
Debt Instrument      
Variable rate, percent | Rate   1.55%  
Mortgages      
Debt Instrument      
Gain (Loss) on Extinguishment of Debt 800,000    
Mortgages | Unsecured Term Loan in 2023      
Debt Instrument      
Repayments of debt $ 200,000,000.0    
Mortgages | LIBOR | Minimum      
Debt Instrument      
Variable rate, percent 1.20%    
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate 1.85%    
Mortgages | LIBOR | Maximum      
Debt Instrument      
Variable rate, percent 1.90%