Common Stock Reserved for Future Issuance (Details) - shares	Sep. 30, 2017	Sep. 30, 2016
Stockholders' equity
Shares reserved for future issuance (in shares)	4,218,016	3,478,305
Common stock warrants
Stockholders' equity
Shares reserved for future issuance (in shares)	24,566	24,566
Stock options
Stockholders' equity
Shares reserved for future issuance (in shares)	3,669,791	3,118,255
Employee Stock Purchase Plan
Stockholders' equity
Shares reserved for future issuance (in shares)	523,659	335,484