DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ / shares in Units, $ in Thousands, $ in Thousands					1 Months Ended	12 Months Ended
	Aug. 21, 2020 USD ($) shares	Aug. 21, 2020 USD ($) shares	Aug. 18, 2020 USD ($) shares	Feb. 19, 2020 USD ($)	Aug. 31, 2020 USD ($) shares	Sep. 30, 2020 USD ($) segment $ / shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2018 USD ($)	Nov. 12, 2020 USD ($)	Sep. 30, 2020 AUD ($)	Sep. 30, 2020 USD ($)	Jun. 08, 2020 USD ($)	Jan. 30, 2020 USD ($)	Jan. 29, 2020 USD ($)	Nov. 30, 2019 USD ($)	Oct. 01, 2019 USD ($)	Sep. 30, 2019 AUD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 CAD ($)	Feb. 06, 2018 USD ($)	Sep. 30, 2017 USD ($)
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Non-service cost components of net periodic benefit cost (credit)						$ (1,559,000)	$ (3,148,000)	$ (3,649,000)
Sale of stock, number of shares issued (in shares) | shares	700,000	8,700,000	8,000,000		8,700,000
Net process from sale of stock	$ 14,335,000	$ 178,165,000	$ 163,830,000		$ 178,165,000
Number of reportable segments | segment						3
Cash in non U.S. bank accounts											$ 55,000,000							$ 34,200,000
Fair value of insurance contracts											3,436,000
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax											5,601,000							(8,460,000)
Defined benefit plan, fair value of plan assets											147,145,000							145,610,000
Change in retained earnings								474,391,000			700,151,000							477,763,000			$ 398,808,000
Percentage of performance obligations recognized at a point in time						86.00%
Percentage of performance obligations recognized over time						14.00%
Customer program reserves and cash discounts netted against accounts receivable											27,607,000							17,322,000
Contract assets, before allowance for credit Loss, noncurrent											7,500,000							13,100,000
Depreciation, depletion and amortization, nonproduction						$ 52,819,000	51,926,000	46,733,000
Accumulated capitalized interest costs								2,896,000			2,520,000							2,925,000
Original cost of fully depreciated property plant and equipment											262,255,000
Fair value projection, term						5 years
Fair value terminal value (in percentage)						3.00%
Operating right-of-use assets											161,627,000
Lease liabilities											167,902,000
Goodwill, impairment loss						$ 0	0	0
Research and development arrangement, contract to perform for others, costs incurred, gross						15,400,000	15,400,000	15,400,000
Selling, general and administrative expenses						486,398,000	447,163,000	418,517,000
Selling, General and Administrative Expenses
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Depreciation						$ 19,656,000	$ 19,026,000	16,306,000
U.S. Government
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Percentage of consolidated accounts receivable						9.00%
Home Depot
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Percentage of consolidated accounts receivable						18.00%
Fair Value, Inputs, Level 2 | Estimate of Fair Value Measurement
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Trading securities											1,703,000							1,518,000
Fair Value, Inputs, Level 2 | Portion at other than Fair Value Measurement
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Trading securities											1,000,000							1,000,000
Senior Notes Due 2028
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Debt instrument, face amount				$ 850,000,000								$ 150,000,000
Stated percentage				5.75%
Issuance price, percentage				100.25%
Senior Notes Due 2028 | Fair Value, Inputs, Level 1
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Long-term debt, fair value											1,040,000,000
Senior Notes Due 2022
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Stated percentage				5.25%
Extinguishment of debt, amount				$ 1,000,000,000
Minimum
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Fair value discount rates (in percentage)						7.10%
Finite-lived intangible asset, useful life						8 years
Minimum | Building and Building Improvements
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life						25 years
Minimum | Machinery and equipment
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life						2 years
Maximum
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Maturity period of highly liquid investments						3 months
Fair value discount rates (in percentage)						9.00%
Finite-lived intangible asset, useful life						25 years
Maximum | Building and Building Improvements
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life						40 years
Maximum | Machinery and equipment
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life						15 years
Australian Dollar Contracts | Designated as hedging instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Derivative, notional amount										$ 32,000							$ 14,000
Contracts weighted average rate price (in dollars per share) | $ / shares						$ 1.41	$ 1.48
Accumulated other comprehensive income (loss), foreign currency translation adjustment, before tax											168,000							327,000
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax											109,000							213,000
Gain (loss) on hedging activity						$ (2,163,000)	$ 1,361,000
Australian Dollar Contracts | Minimum | Designated as hedging instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Contracts expiration days						30 days
Australian Dollar Contracts | Maximum | Designated as hedging instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Contracts expiration days						146 days
Canadian Dollar Contract | Not Designated as Hedging Instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Derivative, notional amount											7,900,000								$ 3,500
Contracts weighted average rate price (in dollars per share) | $ / shares						$ 1.33	$ 1.32
Fair value gain (loss) on foreign currency contract not qualify for hedge accounting						$ (92,000)	$ 14,000
Canadian Dollar Contract | Fair Value, Inputs, Level 2 | Not Designated as Hedging Instrument | Other Income
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Gain (loss) on sale of derivatives						$ 189,000	68,000
Canadian Dollar Contract | Minimum | Not Designated as Hedging Instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Term of contract						30 days
Canadian Dollar Contract | Maximum | Not Designated as Hedging Instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Term of contract						360 days
Great Britain Pound Contracts | Not Designated as Hedging Instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Derivative, notional amount											5,400,000
Fair value gain (loss) on foreign currency contract not qualify for hedge accounting						$ 39,000
Great Britain Pound Contracts | Fair Value, Inputs, Level 2 | Not Designated as Hedging Instrument | Other Income
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Gain (loss) on sale of derivatives						$ 0
Great Britain Pound Contracts | Minimum | Not Designated as Hedging Instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Term of contract						2 days
Great Britain Pound Contracts | Maximum | Not Designated as Hedging Instrument
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Contracts weighted average rate price (in dollars per share) | $ / shares						$ 0.77
Term of contract						208 days
Foreign currency translation adjustments
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Change in retained earnings											$ (25,683,000)							$ (31,284,000)
Shipping and Handling
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Selling, general and administrative expenses						$ 54,500,000	53,500,000	41,700,000
Advertising
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Selling, general and administrative expenses						$ 19,000,000	$ 20,000,000	21,000,000
Cumulative Effect, Period of Adoption, Adjustment
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Change in retained earnings								$ (5,618,000)
Operating right-of-use assets																$ 163,552,000
Lease liabilities																$ 163,676,000
Revolver Due 2025
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Maximum borrowing capacity													$ 400,000,000	$ 350,000,000
PPC | Discontinued Operations, Disposed of by Sale
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Disposal group, including discontinued operation, consideration																				$ 465,000,000
One Time Charges
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost															$ 35,000,000
One Time Charges | Subsequent Event
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost									$ 65,000,000
Capital Investments
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost															$ 40,000,000
Capital Investments | Subsequent Event
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost									65,000,000
Employee Severance and Facility Closing | Subsequent Event
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost									46,000,000
Personnel Related Costs | Subsequent Event
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost									26,000,000
Facilities, Exit Costs and Other | Subsequent Event
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost									20,000,000
Asset Write-Downs | Subsequent Event
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring and related cost									$ 19,000,000
Accounting Standards Update 2016-02
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Accounting Standards Update [Extensible List]						us-gaap:AccountingStandardsUpdate201602Member