Credit Facility (Details) - Credit Facility		3 Months Ended		6 Months Ended
	Oct. 31, 2018	Jan. 31, 2021 USD ($)	Jan. 31, 2020 USD ($)	Jan. 31, 2021 USD ($)	Jan. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Accordion feature		$ 250,000,000		$ 250,000,000
Triggering event debt issuance amount		5,000,000		$ 5,000,000
Triggering event period				91 days
Credit facility amount outstanding		208,000,000		$ 208,000,000
Outstanding standby letters of credit at period end		2,991,000		2,991,000
Outstanding balance during period, minimum				125,000,000
Outstanding balance during period, maximum				217,000,000
Debt issuance costs, net		2,023,000		2,023,000
Interest expense related to credit facility		$ 1,414,000	$ 1,572,000	$ 2,525,000	$ 3,325,000
Weighted average interest rate		2.73%	4.33%	2.71%	4.51%
Maximum Secured Leverage Ratio	3.75			3.75
Maximum Total Leverage Ratio	4.50
Minimum Interest Expense Coverage Ratio	3.25			3.25
Actual Secured Leverage Ratio				3.00
Actual Interest Expense Coverage Ratio				12.45
Adjusted LIBO Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate				1.00%
Federal Funds Effective Swap Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate				0.50%
Secured Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 550,000,000		$ 550,000,000
Revolving Loan Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		300,000,000		300,000,000
Letter of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		35,000,000		35,000,000
Swingline Loan
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 25,000,000		$ 25,000,000