Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common stock	Additional paid-in capital	Accumulated other comprehensive loss [Member]	Accumulated deficit	Total
Beginning Balance at Dec. 31, 2018	$ 22	$ 216,931		$ (175,888)	$ 41,065
Beginning balance (in shares) at Dec. 31, 2018	22,369,036
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options and vesting restricted stock	$ 1	1,910			1,911
Exercise of common stock options and vesting restricted stock (in shares)	318,770
Sale of common stock in at-the-market offering	$ 2	48,017			48,019
Sale of common stock in at-the-market offering (in shares)	2,186,163
ESPP stock purchase		393			393
ESPP stock purchase (in shares)	20,050
Stock-based compensation expense		2,885			2,885
Net loss				(19,968)	(19,968)
Ending Balance at Jun. 30, 2019	$ 25	270,136		(195,416)	74,745
Ending Balance (in shares) at Jun. 30, 2019	24,894,019
Beginning Balance at Mar. 31, 2019	$ 23	219,045		(184,853)	34,215
Beginning balance (in shares) at Mar. 31, 2019	22,491,447
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options and vesting restricted stock		1,408			1,408
Exercise of common stock options and vesting restricted stock (in shares)	216,409
Sale of common stock in at-the-market offering	$ 2	48,017			48,019
Sale of common stock in at-the-market offering (in shares)	2,186,163
ESPP stock purchase		65			65
Stock-based compensation expense		1,601			1,601
Net loss				(10,563)	(10,563)
Ending Balance at Jun. 30, 2019	$ 25	270,136		(195,416)	74,745
Ending Balance (in shares) at Jun. 30, 2019	24,894,019
Increase (Decrease) in Stockholders' Equity
Cumulative-effect adjustment for the adoption of ASC 606				440	440
Beginning Balance at Dec. 31, 2019	$ 28	345,027	$ (153)	(216,244)	128,658
Beginning balance (in shares) at Dec. 31, 2019	28,112,201
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options and vesting restricted stock		1,111			1,111
Exercise of common stock options and vesting restricted stock (in shares)	246,386
ESPP stock purchase		440			440
ESPP stock purchase (in shares)	22,693
Stock-based compensation expense		4,610			4,610
Cumulative translation adjustment			127		127
Net loss				(23,912)	(23,912)
Ending Balance at Jun. 30, 2020	$ 28	351,188	(26)	(240,156)	111,034
Ending Balance (in shares) at Jun. 30, 2020	28,381,280
Beginning Balance at Mar. 31, 2020	$ 28	348,072	(1,200)	(227,854)	119,046
Beginning balance (in shares) at Mar. 31, 2020	28,243,442
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options and vesting restricted stock		615			615
Exercise of common stock options and vesting restricted stock (in shares)	137,838
Stock-based compensation expense		2,501			2,501
Cumulative translation adjustment			1,174		1,174
Net loss				(12,302)	(12,302)
Ending Balance at Jun. 30, 2020	$ 28	$ 351,188	$ (26)	$ (240,156)	$ 111,034
Ending Balance (in shares) at Jun. 30, 2020	28,381,280