Organization and Summary of Significant Accounting Policies - Accounting Standards Update and Change in Accounting Principle (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Interest expense	$ 16,456	$ 9,972	$ 22,177
Basic earnings (loss) per share (in dollars per share)	$ 0.69	$ 0.89	$ 0.15
Diluted earnings (loss) per share (in dollars per share)	$ 0.53	$ 0.70	$ 0.15
Gross Amount	$ 333,373	$ 316,250	$ 316,250
Unamortized debt discount			0
Deferred financing costs, net			(4,779)
Net carrying amount	360,112	312,903	311,471
Deferred tax asset	25,702	12,145	16,353
Deferred tax liability			(356)
Additional paid-in capital	346,181	345,330	340,508
Retained earnings	$ 431,140	402,006	352,947
Accounting Standards Update 2020-06 | Cumulative Effect, Period of Adoption, Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Interest expense		$ 13,900
Basic earnings (loss) per share (in dollars per share)		$ 0.19
Diluted earnings (loss) per share (in dollars per share)		$ 0.01
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Gross Amount			316,250
Unamortized debt discount			(48,785)
Deferred financing costs, net			(3,279)
Net carrying amount			264,186
Deferred tax asset			9,746
Deferred tax liability			3,684
Additional paid-in capital			403,312
Retained earnings			326,781
Revision of Prior Period, Adjustment | Accounting Standards Update 2020-06
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Gross Amount			0
Unamortized debt discount			48,785
Deferred financing costs, net			(1,500)
Net carrying amount			47,285
Deferred tax asset			6,607
Deferred tax liability			(4,040)
Additional paid-in capital			(62,804)
Retained earnings			$ 26,166