Income Taxes (Details) (USD $)	3 Months Ended	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2011
Income Taxes
Consolidated effective tax rate (as a percent)		35.00%	34.50%	32.90%
Severance and other closing costs			$ 390,000
Income tax benefit on investment losses	1,000,000
Increase in basic and diluted earnings per share (in dollars per share)	$ 0.02
Consolidated effective tax rate excluding impact of investment losses (as a percent)			36.60%
Current
Federal		18,122,000	13,593,000	9,651,000
State		3,010,000	2,144,000	1,595,000
Total		21,483,000	16,162,000	11,843,000
Deferred
Federal		(351,000)	390,000	(1,538,000)
State		223,000	78,000	(124,000)
Total		(368,000)	370,000	(1,806,000)
Canada
Current
Foreign		221,000	324,000	455,000
Deferred
Foreign		(174,000)	(85,000)	(143,000)
Singapore
Current
Foreign		130,000	101,000	138,000
Deferred
Foreign		10,000	(13,000)	(1,000)
Netherlands
Deferred
Foreign		(76,000)
Japan
Current
Foreign				$ 4,000