Intangible Assets (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2015	Apr. 30, 2014	Jul. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 82,995,000		$ 82,995,000		$ 82,995,000
Accumulated amortization	61,457,000		61,457,000		56,775,000
Net carrying amount	21,538,000us-gaap_FiniteLivedIntangibleAssetsNet		21,538,000us-gaap_FiniteLivedIntangibleAssetsNet		26,220,000us-gaap_FiniteLivedIntangibleAssetsNet
Amortization of intangibles	1,561,000us-gaap_AmortizationOfIntangibleAssets	1,560,000us-gaap_AmortizationOfIntangibleAssets	4,682,000us-gaap_AmortizationOfIntangibleAssets	4,724,000us-gaap_AmortizationOfIntangibleAssets
Amortization expense - year one	6,211,000		6,211,000
Amortization expense - year two	4,962,000		4,962,000
Amortization expense - year three	4,782,000		4,782,000
Amortization expense - year four	4,782,000		4,782,000
Amortization expense - year five	862,000		862,000
Technologies
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period			11 years 9 months 18 days		11 years 9 months 18 days
Gross carrying amount	47,370,000		47,370,000		47,370,000
Accumulated amortization	38,533,000		38,533,000		36,240,000
Net carrying amount	8,837,000		8,837,000		11,130,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period			10 years 0 months 0 days		10 years 0 months 0 days
Gross carrying amount	29,831,000		29,831,000		29,831,000
Accumulated amortization	20,244,000		20,244,000		18,031,000
Net carrying amount	9,587,000		9,587,000		11,800,000
Trademarks and other
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period			20 years 0 months 0 days		20 years 0 months 0 days
Gross carrying amount	5,794,000		5,794,000		5,794,000
Accumulated amortization	2,680,000		2,680,000		2,504,000
Net carrying amount	$ 3,114,000		$ 3,114,000		$ 3,290,000

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References