Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Detail)	Sep. 30, 2017 shares
Class Of Stock [Line Items]
Total reserved shares of common stock	11,413,298
2014 Equity Incentive Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	10,310,669
2014 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	827,629
Options Issued Outside the 2014 EIP
Class Of Stock [Line Items]
Total reserved shares of common stock	275,000