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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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. 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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Weighted average period before the next renewal or extension (both explicit and implicit) for intangible assets that have been renewed or extended, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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Amount of noncash expense for share-based payment arrangement.

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BUSINESS COMBINATION - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 15, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Acquisition of business, net of cash acquired		$ 0	$ 1,182,187	$ 0
Goodwill		718,647	710,071	101,083
Share-based compensation expense		16,396	18,227	18,517
Non-cash charge on inventory step up of acquired inventory sold		0	14,869	0
Wood Treatment
Business Acquisition [Line Items]
Goodwill		35,000
Acquisition-related costs
Business Acquisition [Line Items]
Non-cash charge on inventory step up of acquired inventory sold			0	14,869
Electronic Materials
Business Acquisition [Line Items]
Goodwill		360,425	352,797	96,083
Performance Materials
Business Acquisition [Line Items]
Goodwill		$ 358,222	357,274	5,000
KMG
Business Acquisition [Line Items]
Acquisition of business, net of cash acquired	$ 1,513,235
Consideration transferred	1,536,452
Cash acquired from acquisition	$ 23,217
Weighted average useful life	17 years 10 months 24 days
KMG \| Acquisition-related costs
Business Acquisition [Line Items]
Non-recurring transaction cost			2,495	33,208
Share-based compensation expense			$ 427	$ 38,132
KMG \| Electronic Materials
Business Acquisition [Line Items]
Goodwill	$ 259,859
KMG \| Performance Materials
Business Acquisition [Line Items]
Goodwill	$ 353,475