Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Class A	Common Class B	Common Stock Common Class A	Common Stock Common Class B	Treasury Stock	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Sep. 30, 2022				155,157,220	100
Treasury stock, beginning balance (in shares) at Sep. 30, 2022						4,116,570
Beginning balance at Sep. 30, 2022	$ 1,430,707			$ 155	$ 0	$ (73,088)	$ 1,630,378	$ (126,738)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,130							23,130
Other comprehensive income (loss)	691								691
Stock-based compensation	13,607						13,607
Exercise of vested stock options (in shares)				483,074
Exercise of vested stock options	11,111			$ 1			11,110
Issuance of common stock under employee stock plan, net of shares withheld for taxes (in shares)				148,053
Issuance of common stock under employee stock plan, net of shares withheld for taxes	(1,381)						(1,381)
Cancellation of restricted stock awards (in shares)				(19,306)
Treasury stock purchases (in shares)		2,300,000				2,299,507
Treasury stock purchases	(55,968)	$ (55,968)				$ (55,968)
Ending balance at Jun. 30, 2023	1,421,897			$ 156	$ 0	$ (129,056)	1,653,714	(103,608)	691
Treasury stock, ending balance (in shares) at Jun. 30, 2023						6,416,077
Ending balance (in shares) at Jun. 30, 2023				155,769,041	100
Beginning balance (in shares) at Mar. 31, 2023				155,303,433	100
Treasury stock, beginning balance (in shares) at Mar. 31, 2023						4,469,330
Beginning balance at Mar. 31, 2023	1,419,390			$ 155	$ 0	$ (80,576)	1,641,321	(138,248)	(3,262)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,640							34,640
Other comprehensive income (loss)	3,953								3,953
Stock-based compensation	4,105						4,105
Exercise of vested stock options (in shares)				400,428
Exercise of vested stock options	9,210			$ 1			9,209
Issuance of common stock under employee stock plan, net of shares withheld for taxes (in shares)				66,158
Issuance of common stock under employee stock plan, net of shares withheld for taxes	(921)						(921)
Cancellation of restricted stock awards (in shares)				(978)
Treasury stock purchases (in shares)		1,947,000				1,946,747
Treasury stock purchases	(48,480)	$ (48,480)				$ (48,480)
Ending balance at Jun. 30, 2023	$ 1,421,897			$ 156	$ 0	$ (129,056)	1,653,714	(103,608)	691
Treasury stock, ending balance (in shares) at Jun. 30, 2023						6,416,077
Ending balance (in shares) at Jun. 30, 2023				155,769,041	100
Beginning balance (in shares) at Sep. 30, 2023			100	155,967,736	100
Treasury stock, beginning balance (in shares) at Sep. 30, 2023	8,268,423					8,268,423
Beginning balance at Sep. 30, 2023	$ 1,410,313			$ 156	$ 0	$ (189,666)	1,662,322	(64,377)	1,878
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	125,016							125,016
Other comprehensive income (loss)	(951)								(951)
Stock-based compensation	20,684						20,684
Exercise of vested stock options (in shares)				803,446
Exercise of vested stock options	19,419			$ 1			19,418
Issuance of common stock under employee stock plan, net of shares withheld for taxes (in shares)				300,944
Issuance of common stock under employee stock plan, net of shares withheld for taxes	(4,853)						(4,853)
Conversion of Class B common stock into Class A common stock (in shares)				100	(100)
Treasury stock purchases (in shares)		4,110,000				4,109,506
Treasury stock purchases	(176,616)	$ (176,615)				$ (163,784)	(12,832)
Ending balance at Jun. 30, 2024	$ 1,393,012			$ 157	$ 0	$ (353,450)	1,684,739	60,639	927
Treasury stock, ending balance (in shares) at Jun. 30, 2024	12,377,929					12,377,929
Ending balance (in shares) at Jun. 30, 2024			0	157,072,226	0
Beginning balance (in shares) at Mar. 31, 2024				157,010,677	0
Treasury stock, beginning balance (in shares) at Mar. 31, 2024						11,520,848
Beginning balance at Mar. 31, 2024	$ 1,386,931			$ 157	$ 0	$ (313,050)	1,688,604	10,529	691
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50,110							50,110
Other comprehensive income (loss)	236								236
Stock-based compensation	5,997						5,997
Exercise of vested stock options (in shares)				34,346
Exercise of vested stock options	790						790
Issuance of common stock under employee stock plan, net of shares withheld for taxes (in shares)				27,203
Issuance of common stock under employee stock plan, net of shares withheld for taxes	(652)						(652)
Treasury stock purchases (in shares)		857,000				857,081
Treasury stock purchases	(50,400)	$ (50,400)				$ (40,400)	(10,000)
Ending balance at Jun. 30, 2024	$ 1,393,012			$ 157	$ 0	$ (353,450)	$ 1,684,739	$ 60,639	$ 927
Treasury stock, ending balance (in shares) at Jun. 30, 2024	12,377,929					12,377,929
Ending balance (in shares) at Jun. 30, 2024			0	157,072,226	0