Nature of Operations and Summary of Significant Accounting Policies - Potentially Dilutive Common Shares Excluded from Calculation of Net Loss per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	5,137	5,717	5,137	5,717
Stock options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	2,390	3,047	2,390	3,047
RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	2,682	2,670	2,682	2,670
ESPP common stock equivalents
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total potentially dilutive common shares outstanding (in shares)	65	0	65	0