Comprehensive Income (Schedule Of Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2012	Jan. 31, 2011
Comprehensive Income [Abstract]
Net income	$ 13,680	$ 5,688	$ 36,038	$ 29,376
Change in temporary impairment of investments, net of tax	16	23	(15)	155
Comprehensive income	$ 13,696	$ 5,711	$ 36,023	$ 29,531

The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

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

-Publisher FASB

-Name Accounting Standards Codification

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-Section 45

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-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e540-108580

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 30

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

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-Appendix A

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-Name Accounting Research Bulletin (ARB)

-Number 51

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6508144

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6519514

+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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-Publisher FASB

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-Name Accounting Standards Codification

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-Name Accounting Research Bulletin (ARB)

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-Name Statement of Financial Accounting Standard (FAS)

-Number 130

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Research Bulletin (ARB)

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Reference 12: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

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-Publisher FASB

-Name Accounting Standards Codification

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+ Details