Credit Facility (Details) (USD $)	3 Months Ended
	Oct. 31, 2011	Oct. 31, 2010
Credit Facility [Abstract]
Line of credit facility, expiration date	January 31, 2014
Line of credit facility, maximum borrowing capacity	$ 150,000,000
Credit Facility sub-limit for commercial letters of credit	15,000,000
Credit Facility sub-limit for standby letters of credit	35,000,000
Minimum applicable interest rate margin over LIBOR at which the revolving credit facility may bear interest	2.25%
Maximum applicable interest rate margin over LIBOR at which the 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%
Minimum amount of total consolidated indebtedness, if maintained, that would not trigger a minimum level of Consolidated Adjusted EBITDA covenant requirement	200,000,000
Outstanding standby letters of credit at period end	1,392,000
Applicable interest rate margin over LIBOR at period end	2.50%
Applicable interest rate margin over base rate at period end	1.50%
Interest expense related to credit facility	207,000	210,000
Credit facility amendment costs incurred and capitalized in period	$ 249,000