FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENT (Details 2) - USD ($) $ in Thousands	Sep. 30, 2015	Mar. 19, 2015	Sep. 30, 2014
Supplemental fair value information about long-term fixed-rate debt
Carrying value of long-term fixed-rate debt	$ 531,500
Due July 21, 2016
Supplemental fair value information about long-term fixed-rate debt
Debt issued	40,000
Unsecured senior notes issued March 19, 2015
Supplemental fair value information about long-term fixed-rate debt
Debt issued	500,000	$ 500,000
Total Measure at Fair Value
Supplemental fair value information about long-term fixed-rate debt
Carrying value of long-term fixed-rate debt			$ 79,100
Significant Other Observable Inputs (Level 2)
Supplemental fair value information about long-term fixed-rate debt
Fair value of long-term fixed-rate debt	553,500
Significant Other Observable Inputs (Level 2) | Total Measure at Fair Value
Supplemental fair value information about long-term fixed-rate debt
Fair value of long-term fixed-rate debt			$ 84,300
Recurring basis | Total Measure at Fair Value
Short-term investments:
Short-term investments	45,543
Assets:
Cash and cash equivalents	717,977
Investments	91,483
Other current assets	38,095
Other assets	2,000
Total assets measured at fair value	895,098
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments:
Short-term investments	4,823
Assets:
Cash and cash equivalents	717,977
Investments	91,483
Other current assets	37,845
Other assets	2,000
Total assets measured at fair value	854,128
Recurring basis | Significant Other Observable Inputs (Level 2)
Short-term investments:
Short-term investments	40,720
Assets:
Other current assets	250
Total assets measured at fair value	40,970
Recurring basis | Certificate of deposit | Total Measure at Fair Value
Short-term investments:
Short-term investments	2,101
Recurring basis | Certificate of deposit | Significant Other Observable Inputs (Level 2)
Short-term investments:
Short-term investments	2,101
Recurring basis | Corporate debt securities | Total Measure at Fair Value
Short-term investments:
Short-term investments	27,139
Recurring basis | Corporate debt securities | Significant Other Observable Inputs (Level 2)
Short-term investments:
Short-term investments	27,139
Recurring basis | U.S. government and federal agency securities | Total Measure at Fair Value
Short-term investments:
Short-term investments	16,303
Recurring basis | U.S. government and federal agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments:
Short-term investments	4,823
Recurring basis | U.S. government and federal agency securities | Significant Other Observable Inputs (Level 2)
Short-term investments:
Short-term investments	$ 11,480