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BUSINESS COMBINATION - Allocation of Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019	Nov. 15, 2018
Fair values of assets acquired and liabilities assumed [Abstract]
Goodwill	$ 709,823	$ 710,071
KMG
Fair values of assets acquired and liabilities assumed [Abstract]
Cash			$ 23,217
Accounts receivable			63,950
Inventories			68,087
Prepaid expenses and other current assets			14,694
Property, plant and equipment			147,170
Intangible assets			844,800
Other long-term assets			5,805
Accounts payable			(28,835)
Accrued expenses and other current liabilities			(44,216)
Deferred income taxes liabilities			(156,474)
Other long-term liabilities			(15,080)
Total identifiable net assets acquired			923,118
Goodwill			613,334
Total consideration transferred			$ 1,536,452