Credit Facility (Details) (USD $)	3 Months Ended		6 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
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		$ 100,000,000
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 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		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		200,000,000
Outstanding standby letters of credit at period end	1,894,000		1,894,000
Commercial letters of credit outstanding amount	0		0
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 related to credit facility	$ 184,000	$ 244,000	$ 363,000	$ 451,000