Stock-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended				12 Months Ended				1 Months Ended		12 Months Ended			1 Months Ended					1 Months Ended
	Mar. 26, 2012	Mar. 31, 2012	Apr. 30, 2011	Apr. 11, 2011	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2013 Stock Option [Member]	Sep. 24, 2012 Straight Path IP Group, Inc. [Member]	Mar. 15, 2011 Straight Path IP Group, Inc. [Member] Employees	Jul. 31, 2013 Straight Path IP Group, Inc. [Member]	Jul. 31, 2011 Straight Path IP Group, Inc. [Member]	Apr. 30, 2011 Common Stock [Member]	Mar. 26, 2012 Class B Common Stock [Member]	Nov. 22, 2011 Class B Common Stock [Member]	Apr. 11, 2011 Class B Common Stock [Member]	Dec. 31, 2011 Class B Common Stock [Member]	Apr. 30, 2011 Class B Common Stock [Member]	Aug. 31, 2013 Class B Common Stock [Member] Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for award under 2005 Stock Option and Incentive Plan													1,000,000					1,000,000
Shares of common stock available for future grants													100,000					100,000
Shares of common stock reserved for award under 2005 Stock Option and Incentive Plan					5,300,000												1,100,000
Shares of common stock available for future grants					600,000
Stock option awards vesting period								3 years
Stock option awards contractual term								10 years
Weighted-average grant date fair value of options granted during the period						$ 4.97
Total intrinsic value of options exercised during the period					$ 0.2		$ 0.4
Total unrecognized compensation cost					1.0
Total unrecognized compensation cost, Weighted-average period of recognization					3 years 3 months 18 days
Percentage of reduction in the excise price															43.80%				15.29%
Fully vested outstanding options to purchase shares of Class B common stock															500,000				32,155
Stock option expiration period extended	3 years
Extension or replacement applied to options to purchase an aggregate shares of Class B common stock														600,000
Stock-based compensation expense		0.3	0.3								0.7	0.7
Option holder shared ratably to purchase shares of Class B common stock															50,000
Options granted in April 2001 with expiration in April 2011 extended for one year																100,000
Expected volatility				73.00%		66.80%
Discount rate				0.26%		1.46%
Expected term				1 year		6 years 7 months 6 days
Total unrecognized compensation cost related to non-vested stock-based compensation arrangements					4.7
Total unrecognized compensation cost related to non-vested stock-based compensation arrangements, expected weighted-average period					9 months 18 days
Total grant date fair value of shares vested					$ 3.5	$ 5.7	$ 1.6
Percentage of grant approved by the Board of Directors									10.00%
Percentage of granted shares of common stock										5.50%
Stock-based compensation shares granted to number of employees										2