CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 105,973	$ 59,458
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	95,516	70,476
Accretion on Asset Retirement Obligations	406	0
Provision for doubtful accounts	366	(75)
Share-based compensation expense	12,191	15,048
Deferred income tax benefit	(9,469)	(16,760)
Non-cash foreign exchange loss	146	907
Gain on disposal of property, plant and equipment	(338)	(59)
Non-cash charge on inventory step up of acquired inventory sold	0	14,869
Amortization of debt issuance costs	2,345	2,086
Other	(63)	2,201
Changes in operating assets and liabilities:
Accounts receivable	8,130	6,187
Inventories	(16,442)	(19,477)
Prepaid expenses and other assets	9,786	10,831
Accounts payable	(5,591)	(1,558)
Accrued expenses, income taxes payable and other liabilities	1,127	(27,089)
Net cash provided by operating activities	204,083	117,045
Net Cash Provided by (Used in) Investing Activities [Abstract]
Additions to property, plant and equipment	(107,015)	(32,691)
Proceeds from sales of property, plant and equipment	1,587	1,210
Acquisition of a business, net of cash acquired	0	(1,182,186)
Cash settlement of life insurance policy	0	3,959
Net cash used in investing activities	(105,428)	(1,209,708)
Cash flows from financing activities:
Repayment of long-term debt	(17,988)	(102,663)
Repurchases of common stock	(38,121)	(9,468)
Proceeds from issuance of long-term debt	0	1,062,337
Proceeds from revolving line of credit	150,000	0
Debt issuance costs	0	(18,745)
Proceeds from issuance of stock	10,960	11,349
Dividends paid	(37,527)	(34,132)
Other financing activities	(123)	0
Net cash provided by financing activities	67,201	908,678
Effect of exchange rate changes on cash	357	(258)
Increase (decrease) in cash and cash equivalents	166,213	(184,243)
Cash and cash equivalents at beginning of period	188,495	352,921
Cash and cash equivalents at end of period	354,708	168,678
Supplemental Cash Flow Information:
Purchases of property, plant and equipment in accrued liabilities and accounts payable at the end of the period	9,609	3,085
Equity consideration related to the acquisition of KMG Chemicals, Inc	0	331,048
Cash paid during the period for lease liabilities	5,647	0
Right of use asset obtained in exchange for lease liabilities	$ 6,351	$ 0