Discontinued Operations - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Jul. 31, 2013
Straight Path Spectrum Inc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage at the time of spin-off	100.00%
Straight Path IP Group Inc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage at the time of spin-off	84.50%
Straight Path Communications Inc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operations amount funded to spin-off	$ 15.00
Straight Path [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reduction of selling, general and administrative expense	0.3
Receivable from subsidiaries included in other current assets	$ 0.2