Credit Facility (Details) (USD $)	3 Months Ended
	Oct. 31, 2012	Oct. 31, 2011
Line of Credit Facility [Abstract]
Line of credit facility, expiration date	Apr. 30, 2014
Date the credit facility may be extended to	Dec. 31, 2016
Line of credit facility, maximum borrowing capacity	$ 100,000,000
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	1.75%
Maximum applicable interest rate margin over LIBOR at which the revolving credit facility may bear interest	2.50%
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	2.00%
Minimum applicable interest rate margin over the base rate at which the credit facility may bear interest	0.75%
Maximum applicable interest rate margin over the base rate at which the credit facility may bear interest	1.50%
Amount an acquisition target purchase price must exceed in order to provide for the target's historical EBITDA to be included when determining compliance with debt covenants	10,000,000
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	1,303,000
Outstanding commercial letters of credit at period end	54,000
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	$ 179,000	$ 207,000