CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common shares	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit	Series A convertible preferred shares Convertible preferred shares	Series B convertible preferred shares Convertible preferred shares
Balance at beginning of period (shares) at Dec. 31, 2017		45,017				4,963	0
Balance at beginning of period at Dec. 31, 2017	$ 11,522	$ 45	$ 136,484	$ (4,695)	$ (120,312)	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(15,072)				(15,072)
Foreign currency translation adjustment	546			546
Unrealized gains/(losses) on investments	1,096			1,096
Stock based compensation expense	3,666		3,666
Issuance of common stock resulting from exercise of stock options (shares)		595
Issuance of common stock resulting from exercise of stock options	983	$ 1	982
Issuance of common stock resulting from exercise of warrants (shares)		157
Issuance of common stock resulting from exercise of warrants	313		313
Issuance of common stock, net of offering costs (shares)		6,325
Issuance of common stock, net of offering costs	47,207	$ 6	47,201
Preferred stock conversion (shares)		2,056				(2,056)
Preferred stock conversion	0	$ 2	(2)
Balance at end of period (shares) at Sep. 30, 2018		54,150				2,907	0
Balance at end of period at Sep. 30, 2018	50,261	$ 54	188,644	(3,053)	(135,384)	$ 0	$ 0
Balance at beginning of period (shares) at Jun. 30, 2018		54,008				2,907	0
Balance at beginning of period at Jun. 30, 2018	55,315	$ 54	187,066	(2,574)	(129,231)	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(6,153)				(6,153)
Foreign currency translation adjustment	27			27
Unrealized gains/(losses) on investments	(506)			(506)
Stock based compensation expense	1,302		1,302
Issuance of common stock resulting from exercise of stock options (shares)		76
Issuance of common stock resulting from exercise of stock options	144	$ 0	144
Issuance of common stock resulting from exercise of warrants (shares)		66
Issuance of common stock resulting from exercise of warrants	132		132
Balance at end of period (shares) at Sep. 30, 2018		54,150				2,907	0
Balance at end of period at Sep. 30, 2018	50,261	$ 54	188,644	(3,053)	(135,384)	$ 0	$ 0
Balance at beginning of period (shares) at Dec. 31, 2018		54,151				2,907	0
Balance at beginning of period at Dec. 31, 2018	39,935	$ 54	189,929	(2,982)	(147,066)	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(24,698)				(24,698)
Foreign currency translation adjustment	1,908			1,908
Unrealized gains/(losses) on investments	377			377
Stock based compensation expense	4,260		4,260
Issuance of common stock resulting from exercise of stock options (shares)		111
Issuance of common stock resulting from exercise of stock options	218	$ 0	218
Issuance of common stock from employee stock purchase plan (in shares)		58
Issuance of common stock from employee stock purchase plan	178		178
Issuance of common stock resulting from exercise of warrants (shares)		73
Issuance of common stock resulting from exercise of warrants	105		105
Preferred stock conversion (shares)		(5,000)					5,000
Preferred stock conversion	0	$ (5)	5
Balance at end of period (shares) at Sep. 30, 2019		49,393				2,907	5,000
Balance at end of period at Sep. 30, 2019	20,642	$ 49	194,695	(697)	(173,405)	$ 0	$ 0
Balance at beginning of period (shares) at Jun. 30, 2019		49,262				2,907	5,000
Balance at beginning of period at Jun. 30, 2019	19,485	$ 49	192,956	(2,707)	(170,813)	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(2,592)				(2,592)
Foreign currency translation adjustment	1,636			1,636
Unrealized gains/(losses) on investments	374			374
Stock based compensation expense	1,518		1,518
Issuance of common stock resulting from exercise of stock options (shares)		61
Issuance of common stock resulting from exercise of stock options	121	$ 0	121
Issuance of common stock resulting from exercise of warrants (shares)		70
Issuance of common stock resulting from exercise of warrants	100		100
Balance at end of period (shares) at Sep. 30, 2019		49,393				2,907	5,000
Balance at end of period at Sep. 30, 2019	$ 20,642	$ 49	$ 194,695	$ (697)	$ (173,405)	$ 0	$ 0