FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Assets [Abstract]
Cash and cash equivalents	$ 363,902	$ 287,479
Other long-term investments	1,153	1,028
Derivative financial instruments	261	28
Total assets	365,316	288,535
Liabilities [Abstract]
Derivative financial instruments	822	1,469
Total liabilities	822	1,469
Level 1 [Member]
Assets [Abstract]
Cash and cash equivalents	363,902	287,479
Other long-term investments	1,153	1,028
Derivative financial instruments	0	0
Total assets	365,055	288,507
Liabilities [Abstract]
Derivative financial instruments	0	0
Total liabilities	0	0
Level 2 [Member]
Assets [Abstract]
Cash and cash equivalents	0	0
Other long-term investments	0	0
Derivative financial instruments	261	28
Total assets	261	28
Liabilities [Abstract]
Derivative financial instruments	822	1,469
Total liabilities	822	1,469
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