INCOME TAXES - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense / federal statutory rate	$ 44,000	$ 17,745	$ 19,598
State and local taxes — net of federal expense	11,156	2,977	6,906
Change in valuation allowance	(3,243)	597	(350)
Stock-based compensation	(2,804)	721	145
Non-deductible transaction costs	5,382	0	0
Executive compensation	3,026	608	364
Federal research and development credit	(2,405)	(746)	(703)
Meals and entertainment	566	284	224
Other	467	(48)	(18)
Income tax expense	$ 56,145	$ 22,138	$ 26,166
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax expense / federal statutory rate	21.00%	21.00%	21.00%
State and local taxes — net of federal expense	5.30%	3.50%	7.40%
Change in valuation allowance	(1.50%)	0.70%	(0.40%)
Stock-based compensation	(1.30%)	0.90%	0.20%
Non-deductible transaction costs	2.70%	0.00%	0.00%
Executive compensation	1.50%	0.70%	0.40%
Federal research and development credit	(1.10%)	(0.80%)	(0.80%)
Meals and entertainment	0.30%	0.30%	0.20%
Other	(0.10%)	(0.10%)	0.00%
Effective tax rate	26.80%	26.20%	28.00%