Credit Facility (Details)		3 Months Ended		9 Months Ended
	Apr. 30, 2020 USD ($)	Apr. 30, 2020 USD ($)	Apr. 30, 2019 USD ($)	Apr. 30, 2020 USD ($)	Apr. 30, 2019 USD ($)	Jul. 31, 2020 USD ($)	Oct. 31, 2018 USD ($)
Line of Credit Facility [Line Items]
Write-off of deferred financing costs		$ 0	$ 0	$ 0	$ 3,217,000
New debt issuance maximum amount	$ 5,000,000	5,000,000		$ 5,000,000
Triggering event, days before maturity of old debt				91 days
Long-term line of credit	159,400,000	159,400,000		$ 159,400,000
Secured Credit Facility
Line of Credit Facility [Line Items]
Write-off of deferred financing costs					3,217,000
Capitalized deferred financing costs							$ 1,813,000
Secured credit facility, maximum borrowing capacity	550,000,000	550,000,000		550,000,000
Outstanding standby letters of credit at period end	2,672,000	2,672,000		2,672,000
Outstanding commercial letters of credit at period end	0	0		0
Unamortized deferred financing costs	$ 2,575,000	2,575,000		2,575,000
Interest expense including amortization of deferred financing costs		$ 1,470,000	$ 2,067,000	$ 4,795,000	$ 6,780,000
Blended interest rate (percent)		3.73%	5.00%	4.24%	5.36%
Maximum Secured Leverage Ratio	3.75	3.75		3.75
Maximum Total Leverage Ratio	4.5	4.5		4.5
Minimum Interest Expense Coverage Ratio	3.25
Secured Leverage Ratio	1.93	1.93		1.93
Interest Expense Coverage Ratio	13.37
Revolving Loan Facility | Secured Credit Facility
Line of Credit Facility [Line Items]
Secured credit facility, maximum borrowing capacity	$ 300,000,000	$ 300,000,000		$ 300,000,000
Line of credit facility, accordion feature	250,000,000	250,000,000		250,000,000
Swingline Loan | Secured Credit Facility
Line of Credit Facility [Line Items]
Secured credit facility, maximum borrowing capacity	25,000,000	25,000,000		25,000,000
Letter of Credit | Secured Credit Facility
Line of Credit Facility [Line Items]
Secured credit facility, maximum borrowing capacity	$ 35,000,000	$ 35,000,000		35,000,000
October 2018 Credit Facility
Line of Credit Facility [Line Items]
Minimum amount outstanding during period				137,000,000
Maximum amount outstanding during period				$ 174,000,000
Federal Funds Effective Rate | Revolving Loan Facility | Secured Credit Facility
Line of Credit Facility [Line Items]
Variable interest rate (percent)				0.50%
Adjusted LIBO rate | Revolving Loan Facility | Secured Credit Facility
Line of Credit Facility [Line Items]
Variable interest rate (percent)				1.00%
Forecast | Secured Credit Facility
Line of Credit Facility [Line Items]
Secured credit facility, maximum borrowing capacity						$ 800,000,000