FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Assets [Abstract]
Available-For-Sale Securities	$ 48,272	$ 0
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets [Abstract]
Available-For-Sale Securities	3,082
Asset-backed Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	4,458
Certificates of Deposit [Member]
Assets [Abstract]
Available-For-Sale Securities	6,299
Corporate Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	25,455
US Treasury Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	8,481
US Government Agencies Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	497
Recurring [Member]
Assets [Abstract]
Cash and cash equivalents	377,230	397,890
Other long-term investments	1,157	929
Derivative financial instruments	379	263
Total assets	427,038	399,082
Liabilities [Abstract]
Derivative financial instruments	6,046	1,881
Total liabilities	6,046	1,881
Recurring [Member] \| Level 1 [Member]
Assets [Abstract]
Cash and cash equivalents	377,230	397,890
Other long-term investments	1,157	929
Derivative financial instruments	0	0
Total assets	378,387	398,819
Liabilities [Abstract]
Derivative financial instruments	0	0
Total liabilities	0	0
Recurring [Member] \| Level 1 [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 1 [Member] \| Asset-backed Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 1 [Member] \| Certificates of Deposit [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 1 [Member] \| Corporate Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 1 [Member] \| US Treasury Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 1 [Member] \| US Government Agencies Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 2 [Member]
Assets [Abstract]
Cash and cash equivalents	0	0
Other long-term investments	0	0
Derivative financial instruments	379	263
Total assets	48,651	263
Liabilities [Abstract]
Derivative financial instruments	6,046	1,881
Total liabilities	6,046	1,881
Recurring [Member] \| Level 2 [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets [Abstract]
Available-For-Sale Securities	3,082
Recurring [Member] \| Level 2 [Member] \| Asset-backed Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	4,458
Recurring [Member] \| Level 2 [Member] \| Certificates of Deposit [Member]
Assets [Abstract]
Available-For-Sale Securities	6,299
Recurring [Member] \| Level 2 [Member] \| Corporate Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	25,455
Recurring [Member] \| Level 2 [Member] \| US Treasury Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	8,481
Recurring [Member] \| Level 2 [Member] \| US Government Agencies Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	497
Recurring [Member] \| Level 3 [Member]
Assets [Abstract]
Cash and cash equivalents	0	0
Other long-term investments	0	0
Derivative financial instruments	0	0
Total assets	0	0
Liabilities [Abstract]
Derivative financial instruments	0	0
Total liabilities	0	$ 0
Recurring [Member] \| Level 3 [Member] \| Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 3 [Member] \| Asset-backed Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 3 [Member] \| Certificates of Deposit [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 3 [Member] \| Corporate Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 3 [Member] \| US Treasury Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	0
Recurring [Member] \| Level 3 [Member] \| US Government Agencies Debt Securities [Member]
Assets [Abstract]
Available-For-Sale Securities	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investments in debt securities classified as available-for-sale, expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

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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.

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Amount of long-term investments classified as other.

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