Secured Credit Facility (Details)		3 Months Ended			6 Months Ended
	Jan. 31, 2019 USD ($)	Jan. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Jan. 31, 2018 USD ($)	Jan. 31, 2019 USD ($)	Jan. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Feb. 23, 2016 USD ($)
Line of Credit Facility [Line Items]
Write-off of deferred financing costs		$ 0	$ 3,217,000	$ 0	$ 3,217,000	$ 0
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	174,500,000	174,500,000			$ 174,500,000
Current portion of long-term debt	0	0			0		$ 17,211,000
Non-current portion of long-term debt, net	174,500,000	174,500,000			174,500,000		148,087,000
Secured Credit Facility
Line of Credit Facility [Line Items]
Deferred financing costs			1,812,000
Secured credit facility, maximum borrowing capacity	550,000,000	550,000,000			550,000,000			$ 400,000,000
Outstanding standby letters of credit at period end	2,331,000	2,331,000			2,331,000
Outstanding commercial letters of credit at period end	0	0			0
Unamortized deferred financing costs	$ 3,495,000	3,495,000			3,495,000
Long-term Debt							165,298,000
Current portion of long-term debt							17,211,000
Non-current portion of long-term debt, net							148,087,000
Interest expense including amortization of deferred financing costs		$ 2,171,000		$ 2,350,000	$ 4,713,000	$ 4,815,000
Blended interest rate (percent)		5.08%		5.10%	5.54%	5.20%
Leverage ratio	3.75
Maximum total leverage ratio	4.50
Fixed charge coverage ratio	3.25
Debt instrument, period decrease	0.25%
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
Term Loan Facility | Secured Credit Facility
Line of Credit Facility [Line Items]
Secured credit facility, maximum borrowing capacity								250,000,000
Long-term debt, gross							120,121,000
Unamortized deferred financing costs							3,427,000
Long-term Debt							116,694,000
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			150,000,000
Line of credit facility, accordion feature	250,000,000	250,000,000			250,000,000
Minimum amount outstanding during period		160,000,000	34,904,000
Maximum amount outstanding during period		174,500,000	$ 63,804,000
Long-term Debt							$ 48,604,000
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			$ 25,000,000
Federal Funds Effective Swap 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%
Minimum | Secured Credit Facility
Line of Credit Facility [Line Items]
Interest expense coverage ratio	12.16
Maximum | Secured Credit Facility
Line of Credit Facility [Line Items]
Leverage ratio	1.85