Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid -in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Shares outstanding (in shares) at Dec. 31, 2017		37,802,556
Beginning balance at Dec. 31, 2017	$ 154,496	$ 38	$ 365,838	$ (211,269)	$ (111)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation expense	8,645		8,645
Sale of common stock, net of issuance costs (in shares)		2,875,000
Sale of common stock, net of issuance costs	59,917	$ 3	59,914
Exercise of common stock options (in shares)		482,190
Exercise of common stock options	1,418		1,418
Exercise of warrants (in shares)		14,647
Issuance of common stock under employee stock purchase plan (in shares)		53,137
Issuance of common stock under employee stock purchase plan	739		739
Foreign currency translation adjustment	54				54
Net loss	(106,658)			(106,658)
Shares outstanding (in shares) at Dec. 31, 2018		41,227,530
Ending balance at Dec. 31, 2018	118,611	$ 41	436,554	(317,927)	(57)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation expense	9,999		9,999
Sale of common stock, net of issuance costs (in shares)		4,250,000
Sale of common stock, net of issuance costs	38,747	$ 5	38,742
Exercise of common stock options (in shares)		254,335
Exercise of common stock options	1,038		1,038
Issuance of common stock under employee stock purchase plan (in shares)		174,297
Issuance of common stock under employee stock purchase plan	1,008		1,008
Issuance of warrants	2,224		2,224
Foreign currency translation adjustment	9				9
Net loss	(110,053)			(110,053)
Shares outstanding (in shares) at Dec. 31, 2019		45,906,162
Ending balance at Dec. 31, 2019	$ 61,583	$ 46	$ 489,565	$ (427,980)	$ (48)