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, 2019	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	4,113	5,457	676
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	1,687	2,806	569
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	2,352	2,580	83
ESPP common stock equivalents
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	74	71	0
ID Checker earnout shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	0	0	24