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Debt - Senior Unsecured Notes (Details) - Senior notes - USD ($)
Mar. 17, 2020
Jun. 30, 2020
Series G and Series H Senior Unsecured Notes    
Debt Instrument [Line Items]    
Face amount $ 175,000,000  
Issue price, as a percent of aggregate principal amount 100.00%  
Senior unsecured notes, Series G    
Debt Instrument [Line Items]    
Face amount $ 100,000,000  
Stated rate (as a percent) 3.61% 3.61%
Senior unsecured notes, Series H    
Debt Instrument [Line Items]    
Face amount $ 75,000,000  
Stated rate (as a percent) 3.73% 3.73%