Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Adoption of ASU [Member]	Common Stock [Member] Common Class A [Member]	Common Stock [Member] Common Class B [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Adoption of ASU [Member]
Beginning balance at Sep. 30, 2020	$ 1,303,888		$ 155		$ 1,587,208	$ (283,475)
Beginning balance (in shares) at Sep. 30, 2020			154,637,240	100
Net income (loss)	32,788					32,788
Stock-based compensation	9,931				9,931
Exercise of vested stock options	2,953				2,953
Exercise of vested stock options (in shares)			123,993
Cancellation of restricted stock awards			(21,995)
IPO costs	(210)				(210)
Adoption of ASU 2016-02		$ 2,098					$ 2,098
Ending balance at Mar. 31, 2021	1,351,448		$ 155		1,599,882	(248,589)
Ending balance (in shares) at Mar. 31, 2021			154,739,238	100
Beginning balance at Dec. 31, 2020	1,321,166		$ 155		1,592,240	(271,229)
Beginning balance (in shares) at Dec. 31, 2020			154,735,617	100
Net income (loss)	22,640					22,640
Stock-based compensation	7,052				7,052
Exercise of vested stock options	590				590
Exercise of vested stock options (in shares)			25,616
Cancellation of restricted stock awards			(21,995)
Ending balance at Mar. 31, 2021	1,351,448		$ 155		1,599,882	(248,589)
Ending balance (in shares) at Mar. 31, 2021			154,739,238	100
Beginning balance at Sep. 30, 2021	1,427,164		$ 155		1,615,236	(188,227)
Beginning balance (in shares) at Sep. 30, 2021			154,866,313	100
Net income (loss)	52,525					52,525
Stock-based compensation	8,851				8,851
Exercise of vested stock options	4,923				4,923
Exercise of vested stock options (in shares)			214,041
Cancellation of restricted stock awards			(10,573)
Issuance of common stock under employee stock plan, net of shares withheld for taxes	(429)				(429)
Issuance of common stock under employee stock plan, net of shares withheld for taxes (in shares)			38,846
Ending balance at Mar. 31, 2022	1,493,034		$ 155		1,628,581	(135,702)
Ending balance (in shares) at Mar. 31, 2022			155,108,627	100
Beginning balance at Dec. 31, 2021	1,451,151		$ 155		1,622,516	(171,520)
Beginning balance (in shares) at Dec. 31, 2021			155,032,377	100
Net income (loss)	35,818					35,818
Stock-based compensation	4,881				4,881
Exercise of vested stock options	1,613				1,613
Exercise of vested stock options (in shares)			70,149
Cancellation of restricted stock awards			(6,174)
Issuance of common stock under employee stock plan, net of shares withheld for taxes	(429)				(429)
Issuance of common stock under employee stock plan, net of shares withheld for taxes (in shares)			12,275
Ending balance at Mar. 31, 2022	$ 1,493,034		$ 155		$ 1,628,581	$ (135,702)
Ending balance (in shares) at Mar. 31, 2022			155,108,627	100