Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Jul. 31, 2012
Summary of assets measured at fair value on recurring basis
Available-for-sale securities	$ 10,830
Fair Value, Measured, Recurring Basis [Member]
Summary of assets measured at fair value on recurring basis
Available-for-sale securities	10,830
Fair Value, Measured, Recurring Basis [Member] | Level 1 (1) [Member]
Summary of assets measured at fair value on recurring basis
Available-for-sale securities
Fair Value, Measured, Recurring Basis [Member] | Level 2 (2) [Member]
Summary of assets measured at fair value on recurring basis
Available-for-sale securities	10,830
Fair Value, Measured, Recurring Basis [Member] | Level 3 (3) [Member]
Summary of assets measured at fair value on recurring basis
Available-for-sale securities