Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		$ 8,378	$ 8,002	$ 5,540
Charged to Costs & Expenses		3,441	9,541	6,283
Other Changes Add (Deduct)	[1]	(5,698)	(9,165)	(3,821)
Balance at End of Year		$ 6,121	$ 8,378	$ 8,002

[1] Bad debts written off (net of recoveries).