Summary of Marketable Securities and Related Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jan. 31, 2015	Jul. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Market Value	$ 56,890	$ 39,659
Unrealized Gain/(Loss)	2
Securities Less Than 12 months unrealized losses
Schedule of Available-for-sale Securities [Line Items]
Market Value	9,578	5,101
Unrealized Gain/(Loss)	(27)	(19)
Securities Greater Than 12 months unrealized losses
Schedule of Available-for-sale Securities [Line Items]
Market Value	10,365	9,739
Unrealized Gain/(Loss)	(24)	(24)
Securities Less Than 12 months unrealized gains
Schedule of Available-for-sale Securities [Line Items]
Market Value	16,970	16,677
Unrealized Gain/(Loss)	10	20
Securities Greater Than 12 months unrealized gains
Schedule of Available-for-sale Securities [Line Items]
Market Value	19,977	8,142
Unrealized Gain/(Loss)	$ 43	$ 23