CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Convertible Preferred Stock [Member]	Total
Convertible preferred stock, beginning balance at Dec. 31, 2014					$ 78,467
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2014					4,419,853
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock upon completion of initial public offering					$ (78,467)
Conversion of convertible preferred stock upon completion of initial public offering (in shares)					(4,419,853)
Stockholder's equity (deficit), beginning balance at Dec. 31, 2014		$ 3,912	$ (3)	$ (74,161)		$ (70,252)
Stockholder's equity (deficit), beginning balance (in shares) at Dec. 31, 2014	559,554
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from initial public offering, net of issuance costs	$ 1	22,100				22,101
Proceeds from initial public offering, net of issuance costs (in shares)	5,192,184
Conversion of convertible preferred stock upon completion of initial public offering	$ 1	78,466				78,467
Conversion of convertible preferred stock upon completion of initial public offering (in shares)	9,114,739
Reclassification of warrant liability to additional paid-in capital upon closing of initial public offering		1,892				1,892
Cashless exercise of common stock warrants upon completing of initial public offering (in shares)	102,289
Options exercised		10				10
Options exercised (in shares)	5,952
Stock-based compensation		787				787
Foreign currency translation adjustment			(143)			(143)
Net loss				(8,383)		(8,383)
Stockholder's equity (deficit), ending balance at Dec. 31, 2015	$ 2	107,167	(146)	(82,544)		24,479
Stockholder's equity (deficit), ending balance (in shares) at Dec. 31, 2015	14,974,718
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Options exercised		24				24
Options exercised (in shares)	13,112
Employee stock purchase plan		215				215
Employee stock purchase plan (in shares)	68,392
Restricted stock units (in shares)	438,086
Stock-based compensation		3,343				3,343
Foreign currency translation adjustment			(84)			(84)
Net loss				(11,612)		(11,612)
Stockholder's equity (deficit), ending balance at Dec. 31, 2016	$ 2	110,749	(230)	(94,156)		$ 16,365
Stockholder's equity (deficit), ending balance (in shares) at Dec. 31, 2016	15,494,308					15,494,308
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from follow-on offering, net of issuance costs		18,363				$ 18,363
Proceeds from follow-on offering, net of issuance costs (in shares)	5,000,000
Cashless exercise of common stock warrants (in shares)	10,223
Options exercised		442				442
Options exercised (in shares)	230,123
Employee stock purchase plan		339				339
Employee stock purchase plan (in shares)	110,711
Restricted stock units, net of taxes paid related to net settlement of equity awards		(308)				(308)
Restricted stock units, net of taxes paid related to net settlement of equity awards (in shares)	446,468
Stock-based compensation		3,502				3,502
Foreign currency translation adjustment			(65)			(65)
Net loss				(5,688)		(5,688)
Stockholder's equity (deficit), ending balance at Dec. 31, 2017	$ 2	$ 133,087	$ (295)	$ (99,844)		$ 32,950
Stockholder's equity (deficit), ending balance (in shares) at Dec. 31, 2017	21,291,833					21,291,833