Equity Incentive Plans - Employee Stock Purchase Plan (Details) - Employee Stock - shares	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized (in shares)	1,250,000
Purchase price of common stock (as a percent)	85.00%
Shares available for grant (in shares)	1,123,326
Shares issued under employee stock purchase plan (in shares)	126,674	162,360