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Financial Instruments and Fair Value Measurement - Recurring (Details) - USD ($) $ in Thousands | Mar. 31, 2016 | Sep. 30, 2015
--- | --- | ---
Supplemental fair value information about long-term fixed-rate debt |  |
Carrying value of long-term fixed-rate debt | $ 532,100 | $ 531,500
Fixed-rate debt | 540,000 | 540,000
Unsecured senior notes issued July 21, 2009 |  |
Supplemental fair value information about long-term fixed-rate debt |  |
Fixed-rate debt | 40,000 |
Unsecured senior notes issued March 19, 2015 |  |
Supplemental fair value information about long-term fixed-rate debt |  |
Fixed-rate debt | 500,000 | 500,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis |  |
Short-term investments: |  |
Short-term investments | 16,661 |
Assets: |  |
Cash and cash equivalents | 898,013 |
Investments | 71,158 |
Other current assets | 28,662 |
Other assets | 2,000 |
Total assets measured at fair value | 1,016,494 |
Significant Other Observable Inputs (Level 2) |  |
Supplemental fair value information about long-term fixed-rate debt |  |
Fair value of long-term fixed-rate debt | 533,200 | $ 553,500
Significant Other Observable Inputs (Level 2) | Recurring basis |  |
Short-term investments: |  |
Short-term investments | 28,865 |
Assets: |  |
Other current assets | 250 |
Total assets measured at fair value | 29,115 |
Corporate debt securities | Significant Other Observable Inputs (Level 2) | Recurring basis |  |
Short-term investments: |  |
Short-term investments | 18,427 |
U.S. government and federal agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis |  |
Short-term investments: |  |
Short-term investments | 16,661 |
U.S. government and federal agency securities | Significant Other Observable Inputs (Level 2) | Recurring basis |  |
Short-term investments: |  |
Short-term investments | 10,438 |
Total Measure at Fair Value | Recurring basis |  |
Short-term investments: |  |
Short-term investments | 45,526 |
Assets: |  |
Cash and cash equivalents | 898,013 |
Investments | 71,158 |
Other current assets | 28,912 |
Other assets | 2,000 |
Total assets measured at fair value | 1,045,609 |
Total Measure at Fair Value | Corporate debt securities | Recurring basis |  |
Short-term investments: |  |
Short-term investments | 18,427 |
Total Measure at Fair Value | U.S. government and federal agency securities | Recurring basis |  |
Short-term investments: |  |
Short-term investments | $ 27,099 |

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- Definition Represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with fair value disclosures required in footnote disclosures to financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This element represents the fair value of assets categorized as other current assets which are not in and of themselves material enough to require separate disclosure. + References No definition available. + Details
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + Details
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- Definition Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 + Details
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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7 + Details
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- Definition Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 + Details
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