Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity/(Deficit) - USD ($) $ in Thousands	Total	Series B-1 Convertible Preferred Stock	Series A-2 Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2014	$ (44,429)			$ 8	$ 30,127	$ (74,564)
Temporary equity, Begining balance, Shares at Dec. 31, 2014		3,507,117	1,176,423
Temporary equity, Beginning balance at Dec. 31, 2014		$ 20,081	$ 20,000
Beginning balance, Shares at Dec. 31, 2014				1,538,402
Issuance of Series B-1 convertible preferred stock, net of issuance costs of $6		$ 1,994
Issuance of Series B-1 convertible preferred stock, Shares		340,906
Exercise of stock options	31				31
Exercise of stock options, Shares				45,199
Stock-based compensation	137				137
Net loss	(6,191)					(6,191)
Ending balance at Dec. 31, 2015	(50,452)			$ 8	30,295	(80,755)
Temporary equity, Ending balance, Shares at Dec. 31, 2015		3,848,023	1,176,423
Temporary equity, Ending balance at Dec. 31, 2015		$ 22,075	$ 20,000
Ending balance, Shares at Dec. 31, 2015				1,583,601
Exercise of stock options	25				25
Exercise of stock options, Shares				33,395
Stock-based compensation	83				83
Other comprehensive (loss) income	(2)						$ (2)
Net loss	(6,860)					(6,860)
Ending balance at Dec. 31, 2016	(57,206)			$ 8	30,403	(87,615)	(2)
Temporary equity, Ending balance, Shares at Dec. 31, 2016		3,848,023	1,176,423
Temporary equity, Ending balance at Dec. 31, 2016		$ 22,075	$ 20,000
Ending balance, Shares at Dec. 31, 2016				1,616,996
Issuance of common stock upon IPO, net $3.0 million in commissions and discounts	32,426			$ 16	32,410
Issuance of common stock upon IPO, Shares				3,220,000
IPO costs	(1,870)				(1,870)
Conversion of convertible preferred stock of common stock upon IPO	42,075			$ 23	42,052
Temporary equity conversion of convertible preferred stock of common stock upon IPO, Shares		(3,848,023)	(1,176,423)
Temporary equity conversion of convertible preferred stock of common stock upon IPO		$ (22,075)	$ (20,000)
Conversion of convertible preferred stock of common stock upon IPO, Shares				4,689,753
Reclassification of preferred stock warrant liability into additional paid in capital upon IPO	5,711				5,711
Exercise of stock options	55				55
Exercise of stock options, Shares				74,984
Issuance of common stock in connection with cashless exercise of warrants	1			$ 1
Issuance of common stock in connection with cashless exercise of warrants, Shares				191,263
Issuance of common stock from ESPP purchase	319				319
Issuance of common stock from ESPP purchase, Shares				34,133
Stock-based compensation	628				628
Other comprehensive (loss) income	3						3
Net loss	(9,980)					(9,980)
Ending balance at Dec. 31, 2017	$ 12,162			$ 48	$ 109,708	$ (97,595)	$ 1
Temporary equity, Ending balance, Shares at Dec. 31, 2017		0	0
Ending balance, Shares at Dec. 31, 2017				9,827,129