Credit Facility (Details) - USD ($)		3 Months Ended		6 Months Ended
	Feb. 23, 2016	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015
Uncommitted Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, maximum borrowing capacity		$ 15,000,000		$ 15,000,000
Outstanding standby letters of credit at period end		1,699,000		1,699,000
Outstanding commercial letters of credit at period end		0		0
Interest expense related to Credit Facility		$ 0	$ 0	$ 0
Uncommitted Secured Revolving Credit Facility | Subsequent Event
Line of Credit Facility [Line Items]
Line of Credit Facility, expiration date	Feb. 23, 2016
New Credit Facility | Subsequent Event
Line of Credit Facility [Line Items]
Line of Credit Facility, maximum borrowing capacity	$ 400,000,000
Committed Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, maximum borrowing capacity			$ 100,000,000		$ 100,000,000
Line of Credit Facility, expiration date			Oct. 31, 2014
Interest expense related to Credit Facility					$ 198,000