Convertible Preferred Stock Warrants and Common Stock Warrants - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Mar. 28, 2017	Dec. 31, 2015	Sep. 30, 2015
Class Of Warrant Or Right [Line Items]
Loss on remeasurement of convertible preferred stock warrant liability		$ 3,725,000	$ 524,000
Reclassification of convertible preferred stock warrant liability into additional paid-in capital	$ 5,700,000	5,711,000
Fair value of warrants	300,000		$ 1,875,000		$ 1,351,000
Net proceeds from Initial public offering excluding underwriting discounts and commissions	$ 32,400,000	$ 32,426,000
Series B-1 Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Number of shares called by warrant						173,862
Fair value of warrants						$ 147,000
Series B-1 Convertible Preferred Stock | The March 28, 2017 Preferred stock warrant
Class Of Warrant Or Right [Line Items]
Number of shares called by warrant	61,363			76,704
Fair value of warrants				$ 111,000
Class of warrant, exercise price				$ 5.8667
Warrants Not Settleable in Cash
Class Of Warrant Or Right [Line Items]
Conversion of preferred stock into common stock, shares		191,263
Maximum
Class Of Warrant Or Right [Line Items]
Number of shares called by warrant	84,000
Minimum
Class Of Warrant Or Right [Line Items]
Net proceeds from Initial public offering excluding underwriting discounts and commissions	$ 25,000,000
Other Expense, Net
Class Of Warrant Or Right [Line Items]
Loss on remeasurement of convertible preferred stock warrant liability		$ 3,700,000