Credit Facility (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2011	Apr. 30, 2010
Credit Facility
Line of Credit Facility, Expiration Date			January 31, 2014
Line of Credit Facility, Maximum Borrowing Capacity	$ 150,000,000		$ 150,000,000
Credit Facility sub-limit for commercial letters of credit	15,000,000		15,000,000
Credit Facility sub-limit for standby letters of credit	35,000,000		35,000,000
Minimum applicable interest rate margin over LIBOR at which the unsecured revolving credit facility may bear interest			2.25%
Maximum applicable interest rate margin over LIBOR at which the unsecured revolving credit facility may bear interest			2.75%
Percentage added to the Federal Funds Effective Rate to determine a base rate			0.50%
Basis points added to the daily floating interest rate to determine a base rate			200
Minimum applicable interest rate margin over the base rate at which the credit facility may bear interest			1.25%
Maximum applicable interest rate margin over the base rate at which the credit facility may bear interest			1.75%
Number of prior consecutive quarters considered in determining compliance with financial covenants of credit facility			4
Maximum principal amount of indebtedness for which payment default or acceleration would not trigger credit facility default			7,500,000
Maximum amount of unsatisfied final judgments or orders for the payment of money that would not trigger credit facility default			7,500,000
Minimum percentage of beneficial ownership of voting stock by a person or group resulting from change of control that triggers credit facility default			50.00%
Outstanding standby letters of credit at period end	1,488,000		1,488,000
Applicable interest rate margin over LIBOR at period end	2.50%		2.50%
Applicable interest rate margin over base rate at period end	1.50%		1.50%
Interest expense including amortization of deferred financing charges	203,000	165,000	571,000	464,000
Maximum amount of dividend payments allowed during any four consecutive quarters			30,000,000
Allowance for equity security repurchases and excess dividends over the term of the agreement			100,000,000
Minimum amount of unrestricted cash and cash equivalents required to be maintained			$ 100,000,000