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Line of Credit - Narrative (Details) - Unsecured Revolving Credit Facility - Line of Credit
3 Months Ended
Sep. 20, 2018
USD ($)
loan
term
institution
Mar. 31, 2020
USD ($)
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 500,000,000.0  
Number of financial institutions | institution 4  
Maximum borrowing capacity, per lender $ 125,000,000.0  
Number of extension periods | term 2  
Extension period 12 months  
Additional borrowing capacity $ 250,000,000.0  
Unused commitment fee, percentage 0.20%  
Unused borrowing capacity, fee   $ 800,000
Line of credit, loans outstanding   $ 190,000,000
Eurodollar Loan    
Debt Instrument [Line Items]    
Minimum funding requirement $ 5,000,000.0  
Line of credit, term (or less) 12 months  
Maximum active loan limit | loan 5  
Eurodollar Loan | Minimum | Adjusted LIBOR    
Debt Instrument [Line Items]    
Basis spread on variable rate 0.85%  
Eurodollar Loan | Maximum | Adjusted LIBOR    
Debt Instrument [Line Items]    
Basis spread on variable rate 1.05%  
Alternate Base Rate Loan    
Debt Instrument [Line Items]    
Minimum funding requirement $ 5,000,000.0  
Alternate Base Rate Loan | Adjusted LIBOR    
Debt Instrument [Line Items]    
Basis spread on variable rate 1.00%  
Alternate Base Rate Loan | Federal Reserve Bank of New York    
Debt Instrument [Line Items]    
Basis spread on variable rate 0.50%