Net Income (Loss) Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net income (loss) per share	9,700,000	9,700,000	7,200,000
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net income (loss) per share	2,000,000.0	1,300,000	400,000
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net income (loss) per share	300,000	100,000	200,000