CONDENSED FINANCIAL INFORMATION OF REGISTRANT (PARENT COMPANY ONLY) - Narrative (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Aug. 31, 2024	Feb. 29, 2024
Condensed Statement of Income Captions [Line Items]
Reacquisition cost	$ 244,829	$ 116,578	$ 81,483
Class A
Condensed Statement of Income Captions [Line Items]
Reacquisition cost	244,828	116,578
Open Market | Class A
Condensed Statement of Income Captions [Line Items]
Reacquisition cost	$ 42,900
Accelerated Share Repurchase Agreement | Class A
Condensed Statement of Income Captions [Line Items]
Stock repurchase program, authorized amount				$ 50,000	$ 100,000
Parent Company
Condensed Statement of Income Captions [Line Items]
Minimum threshold percentage of restricted net assets	25.00%
Cash dividends paid	$ 242,500	115,500	73,100
Parent Company | Open Market
Condensed Statement of Income Captions [Line Items]
Reacquisition cost	42,500	79,500	23,100
Parent Company | Second Offering
Condensed Statement of Income Captions [Line Items]
Reacquisition cost		$ 36,000
Parent Company | Accelerated Share Repurchase Agreement
Condensed Statement of Income Captions [Line Items]
Cash dividends paid	242,500
Parent Company | Accelerated Share Repurchase Agreement | Class A
Condensed Statement of Income Captions [Line Items]
Stock repurchase program, authorized amount	$ 200,000		$ 50,000