Net Income Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Oct. 31, 2011	Oct. 31, 2010
Numerator
Net income	$ 32,732	$ 26,281
Restricted stock dividends	(57)	(56)
Preferential dividends	(818)	(820)
Preferential dividends on dilutive stock options	(5)	(6)
Denominator:
Denominator for basic net income per share for both Class A and Class B	52,657	52,448
Plus: Effect of dilutive stock options	297	362
Denominator for diluted net income per share for both Class A and Class B	52,954	52,810
Class A Nonvoting Common Stock [Member]
Numerator
Numerator for basic and diluted net income per share	32,675	26,225
Common stock net income per share calculation:
Basic	$ 0.62	$ 0.50
Diluted	$ 0.62	$ 0.50
Class B Common Stock [Member]
Numerator
Numerator for basic and diluted net income per share	$ 31,852	$ 25,399
Common stock net income per share calculation:
Basic	$ 0.60	$ 0.48
Diluted	$ 0.60	$ 0.48