Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Adoption of ASU [Member]	Common Class A [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, 2019	$ 490,023		$ 75	$ 33	$ 652,493	$ (162,578)
Beginning balance (in shares) at Sep. 30, 2019			75,093,778	33,068,963
Adoption of ASU No. 2016-16		$ 1,336					$ 1,336
Net income (loss)	(9,846)					(9,846)
Stock-based compensation	684				684
Member redemptions prior to initial public offering	(2,201)				(2,201)
Ending balance at Dec. 31, 2019	479,996		$ 75	$ 33	650,976	(171,088)
Ending balance (in shares) at Dec. 31, 2019			75,093,778	33,068,963
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)	10,183					10,183
Stock-based compensation	2,878				2,878
Exercise of vested stock options	2,364				2,364
Exercise of vested stock options (in shares)			98,377
Initial public offering expenses	(210)				(210)
Ending balance at Dec. 31, 2020	$ 1,319,103		$ 155		$ 1,592,240	$ (273,292)
Ending balance (in shares) at Dec. 31, 2020			154,735,617	100