CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Total
Beginning balance at Dec. 31, 2016	$ 2	$ 110,749	$ (230)	$ (94,156)	$ 16,365
Beginning balance (in shares) at Dec. 31, 2016	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				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)
Ending balance at Dec. 31, 2017	$ 2	133,087	(295)	(99,844)	32,950
Ending balance (in shares) at Dec. 31, 2017	21,291,833
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of warrants		4,799			4,799
Proceeds from offering, net of issuance costs	$ 1	42,658			42,659
Proceeds from offering, net of issuance costs (in shares)	7,705,000
Options exercised		280			$ 280
Options exercised (in shares)	112,965				112,965
Employee stock purchase plan		550			$ 550
Employee stock purchase plan (in shares)	125,567
Restricted stock units, net of taxes paid related to net settlement of equity awards		(424)			(424)
Restricted stock units, net of taxes paid related to net settlement of equity awards (in shares)	206,700
Stock-based compensation		3,208			3,208
Foreign currency translation adjustment			160		160
Net loss				(21,440)	(21,440)
Ending balance at Dec. 31, 2018	$ 3	184,158	(135)	(121,284)	$ 62,742
Ending balance (in shares) at Dec. 31, 2018	29,442,065				29,442,065
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Options exercised		378			$ 378
Options exercised (in shares)	112,647				112,647
Employee stock purchase plan		1,193			$ 1,193
Employee stock purchase plan (in shares)	283,931
Restricted stock units, net of taxes paid related to net settlement of equity awards		(582)			(582)
Restricted stock units, net of taxes paid related to net settlement of equity awards (in shares)	430,042
ASC 842 adoption adjustment				248	248
Stock-based compensation		5,697			5,697
Foreign currency translation adjustment			444		444
Purchase of capped calls		(6,150)			(6,150)
Equity component of convertible senior notes (net of issuance costs of $1 million)		21,662			21,662
Net loss				(26,856)	(26,856)
Ending balance at Dec. 31, 2019	$ 3	$ 206,356	$ 309	$ (147,892)	$ 58,776
Ending balance (in shares) at Dec. 31, 2019	30,268,685				30,268,685