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Long-Term Obligations and Commitments - Secured Revolving Credit Facility (Details) - Revolving Credit Facility - 2019 Secured Revolving Credit Facility - USD ($)
9 Months Ended
Feb. 19, 2019
Apr. 30, 2020
Apr. 30, 2019
Debt Instrument [Line Items]      
Periodic interest payment   $ 3,000,000 $ 0
Subsidiary | Line of Credit      
Debt Instrument [Line Items]      
Debt instrument, term 2 years    
Line of credit, maximum borrowing capacity $ 300,000,000    
Interest rate on unused portion of line of credit 0.50%    
Fair value of amount outstanding   $ 48,000,000  
Interest rate at period end   6.04%  
Secured amount   $ 143,000,000  
Subsidiary | Line of Credit | LIBOR      
Debt Instrument [Line Items]      
Basis spread on variable rate 2.39%