Preferred Stock Warrant Liability (Details)	3 Months Ended
	Oct. 28, 2017 $ / shares shares
Class Of Stock [Line Items]
Warrants exercisable and expire	10 years
2012 Financing Arrangements | Series Seed Convertible Preferred Stock
Class Of Stock [Line Items]
Outstanding preferred stock warrants exercised | shares	375,230
Class of warrant, Exercise price of warrants | $ / shares	$ 0.1066
2012 Financing Arrangements | Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Outstanding preferred stock warrants exercised | shares	66,265
Class of warrant, Exercise price of warrants | $ / shares	$ 0.22636
2013 Financing Arrangements | Series A1 Convertible Preferred Stock
Class Of Stock [Line Items]
Outstanding preferred stock warrants exercised | shares	624,730
Class of warrant, Exercise price of warrants | $ / shares	$ 0.2401
2013 Financing Arrangements | Series B Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Outstanding preferred stock warrants exercised | shares	308,315
Class of warrant, Exercise price of warrants | $ / shares	$ 0.486516