The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. 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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Name:	us-gaap_AmortizationOfIntangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Goodwill And Intangible Assets [Line Items]
Amortization	$ 25.2	$ 30.9		$ 78.3	$ 231.7
Minimum [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life				5 years
Maximum [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life				20 years
Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life				28 years 6 months
Allied Acquisition [Member] \| Tradenames [Member]
Goodwill And Intangible Assets [Line Items]
Amortization			$ 142.6