Derivative Instruments - Additional Information (Detail) (Forward Contracts) In Millions, unless otherwise specified	3 Months Ended		3 Months Ended
Oct. 31, 2013 USD ($)	Oct. 31, 2013 CAD	Oct. 31, 2013 Operating Expense USD ($)	Oct. 31, 2012 Operating Expense USD ($)
Derivative [Line Items]
Notional amount of cash flow hedge instruments		3.2
Unrealized loss on cash flow hedge instruments	0.1
Realized gains (losses) on cash flow hedge instruments			$ (0.1)	$ 0.1

Amount of unrealized gain (loss) related to derivatives designated as cash flow hedging instruments, recorded in results of operations to the extent that the cash flow hedge is determined to be ineffective.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

Name:	us-gaap_UnrealizedGainLossOnCashFlowHedgingInstruments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration