Nature of Operations and Summary of Significant Accounting Policies - Potentially Dilutive Common Stocks Excluded From Computation of Basic and Diluted Net Income (Loss) Per Share (Details) - shares shares in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	1,804	4,113	5,457
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	239	1,687	2,806
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	1,519	2,352	2,580
ESPP common stock equivalents
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	14	74	71
Performance RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	32	0	0