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FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Summary of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands | Jun. 30, 2021 | Sep. 30, 2020
--- | --- | ---
Level 3 |  |
Assets: |  |
Non-qualified supplemental savings plan | $ 0 |
Recurring Fair Value Measurements |  |
Assets: |  |
Cash and cash equivalents | 370,553 | $ 487,884
Short-term investments | 187,256 | 89,335
Other current assets | 48,434 | 45,577
Non-qualified supplemental savings plan | 18,556 | 19,819
Debt and equity securities | 18,330 | 11,766
Total investments | 36,886 | 31,585
Other assets | 2,885 | 3,286
Total assets measured at fair value | 646,014 | 657,667
Liabilities: |  |
Contingent earnout liability | 9,796 | 9,123
Recurring Fair Value Measurements | Certificates of deposit |  |
Assets: |  |
Short-term investments |  | 1,370
Recurring Fair Value Measurements | Corporate debt securities |  |
Assets: |  |
Short-term investments | 179,423 | 78,156
Recurring Fair Value Measurements | U.S. government and federal agency securities |  |
Assets: |  |
Short-term investments | 7,833 | 7,817
Recurring Fair Value Measurements | Other |  |
Assets: |  |
Short-term investments |  | 1,992
Recurring Fair Value Measurements | Level 1 |  |
Assets: |  |
Cash and cash equivalents | 370,553 | 487,884
Short-term investments | 7,833 | 9,809
Other current assets | 48,434 | 45,577
Non-qualified supplemental savings plan | 18,556 | 19,819
Debt and equity securities | 14,965 | 7,274
Total investments | 33,521 | 27,093
Other assets | 2,885 | 3,286
Total assets measured at fair value | 463,226 | 573,649
Liabilities: |  |
Contingent earnout liability | 0 | 0
Recurring Fair Value Measurements | Level 1 | Certificates of deposit |  |
Assets: |  |
Short-term investments |  | 0
Recurring Fair Value Measurements | Level 1 | Corporate debt securities |  |
Assets: |  |
Short-term investments | 0 | 0
Recurring Fair Value Measurements | Level 1 | U.S. government and federal agency securities |  |
Assets: |  |
Short-term investments | 7,833 | 7,817
Recurring Fair Value Measurements | Level 1 | Other |  |
Assets: |  |
Short-term investments |  | 1,992
Recurring Fair Value Measurements | Level 2 |  |
Assets: |  |
Cash and cash equivalents | 0 | 0
Short-term investments | 179,423 | 79,526
Other current assets | 0 | 0
Non-qualified supplemental savings plan | 0 | 0
Debt and equity securities | 0 | 3,992
Total investments | 0 | 3,992
Other assets | 0 | 0
Total assets measured at fair value | 179,423 | 83,518
Liabilities: |  |
Contingent earnout liability | 0 | 0
Recurring Fair Value Measurements | Level 2 | Certificates of deposit |  |
Assets: |  |
Short-term investments |  | 1,370
Recurring Fair Value Measurements | Level 2 | Corporate debt securities |  |
Assets: |  |
Short-term investments | 179,423 | 78,156
Recurring Fair Value Measurements | Level 2 | U.S. government and federal agency securities |  |
Assets: |  |
Short-term investments | 0 | 0
Recurring Fair Value Measurements | Level 2 | Other |  |
Assets: |  |
Short-term investments |  | 0
Recurring Fair Value Measurements | Level 3 |  |
Assets: |  |
Cash and cash equivalents | 0 | 0
Short-term investments | 0 | 0
Other current assets | 0 | 0
Non-qualified supplemental savings plan |  | 0
Debt and equity securities | 3,365 | 500
Total investments | 3,365 | 500
Other assets | 0 | 0
Total assets measured at fair value | 3,365 | 500
Liabilities: |  |
Contingent earnout liability | 9,796 | 9,123
Recurring Fair Value Measurements | Level 3 | Certificates of deposit |  |
Assets: |  |
Short-term investments |  | 0
Recurring Fair Value Measurements | Level 3 | Corporate debt securities |  |
Assets: |  |
Short-term investments | 0 | 0
Recurring Fair Value Measurements | Level 3 | U.S. government and federal agency securities |  |
Assets: |  |
Short-term investments | $ 0 | 0
Recurring Fair Value Measurements | Level 3 | Other |  |
Assets: |  |
Short-term investments |  | $ 0

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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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