SEGMENT REPORTING (Details) $ in Thousands	3 Months Ended
Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)
SEGMENT REPORTING [Abstract]
Number of operating segments \| Segment	1
Number of reportable segments \| Segment	2
Revenue from External Customers by Products and Services [Abstract]
Revenue	$ 221,778	$ 139,979
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Adjusted EBITDA - Electronic Materials	74,825	52,897
Adjusted EBITDA - Performance Materials	13,067	1,288
Adjusted EBITDA - Unallocated corporate expenses	(11,042)	(10,852)
Interest income	1,019	951
Interest expense	(6,890)	(1,132)
Depreciation and amortization	(16,541)	(6,500)
Charge for fair value write-up of acquired inventory sold	(10,261)	0
Acquisition and integration related	(27,294)	0
Income before income taxes	16,883	36,652
Electronic Materials [Member]
Revenue from External Customers by Products and Services [Abstract]
Revenue	190,617	133,314
Performance Materials [Member]
Revenue from External Customers by Products and Services [Abstract]
Revenue	$ 31,161	$ 6,665

Earnings before interest, taxes. depreciation and amortization for the Electronic Materials Segment

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Earnings before interest, taxes. depreciation and amortization for the Performance Materials Segment

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Earnings before interest, taxes. depreciation and amortization for Unallocated corporate expenses

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The amount of expense recognized in the current period that reflects the allocation of capitalized costs associated with acquisition of business. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Costs incurred to effect a business combination which have been expensed during the period. Such costs could include business integration costs, systems integration and conversion costs, and severance and other employee-related costs.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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