Net Income Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011	Oct. 31, 2010	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Numerator
Net (loss) income	$ 11,659	$ 27,652	$ (89,954,000)	$ 32,732	$ 29,583	$ 28,589	$ 24,199	$ 26,281	$ (17,911)	$ 108,652	$ 81,956
Less: Restricted stock dividends									(229)	(223)	(147)
Less: Preferential dividends									(818)	(820)	(816)
Preferential dividends on dilutive stock options									(5)	(6)	(11)
Denominator:
Denominator for basic net income (loss) per share for both Class A and Class B									52,453	52,639	52,402
Plus: Effect of dilutive stock options										494	544
Denominator for diluted net income (loss) per share for both Class A and Class B									52,453	53,133	52,946
Class A Nonvoting Common Stock [Member]
Numerator
Numerator for basic and diluted Class A net income (loss) per share									(18,140)	108,429	81,809
Common stock net income (loss) per share calculation:
Basic	$ 0.22	$ 0.53	$ (1.72)	$ 0.62	$ 0.56	$ 0.54	$ 0.46	$ 0.50	$ (0.35)	$ 2.06	$ 1.56
Diluted	$ 0.22	$ 0.52	$ (1.72)	$ 0.62	$ 0.56	$ 0.54	$ 0.46	$ 0.50	$ (0.35)	$ 2.04	$ 1.55
Class B common stock [Member]
Numerator
Numerator for basic and diluted Class A net income (loss) per share									$ (18,963)	$ 107,603	$ 80,982
Common stock net income (loss) per share calculation:
Basic									$ (0.36)	$ 2.04	$ 1.55
Diluted									$ (0.36)	$ 2.03	$ 1.53