CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive (Loss) Gain [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 33,794	$ 212	$ 56,674	$ (3)	$ (23,089)
Balance (in shares) at Dec. 31, 2017		10,699
Net loss	(20,774)				(20,774)
Unrealized gain on short-term investments	7			7
Share-based compensation	753		753
Issuance of common stock upon exercise of stock options	371	$ 2	369
Issuance of common stock upon exercise of stock option (in shares)		62
Balance at Sep. 30, 2018	14,151	$ 214	57,796	4	(43,863)
Balance (in shares) at Sep. 30, 2018		10,761
Balance at Jun. 30, 2018	17,795	$ 214	57,189	2	(39,610)
Balance (in shares) at Jun. 30, 2018		10,748
Net loss	(4,253)				(4,253)
Unrealized gain on short-term investments	2			2
Share-based compensation	587		587
Issuance of common stock upon exercise of stock options	20		20
Issuance of common stock upon exercise of stock option (in shares)		13
Balance at Sep. 30, 2018	14,151	$ 214	57,796	$ 4	(43,863)
Balance (in shares) at Sep. 30, 2018		10,761
Balance at Dec. 31, 2018	13,642	$ 214	58,302		(44,874)
Balance (in shares) at Dec. 31, 2018		10,762
Net loss	(15,002)				(15,002)
Treasury stock (in shares)		(43)
Share-based compensation	1,185		1,185
Redomiciliation share exchange		$ (203)	203
Issuance of restricted common stock and option, net of issuance costs	15,545	$ 2	15,543
Issuance of restricted common stock and option, net of issuance costs (in shares)		2,400
Issuance of common stock, net of issuance costs	21,278	$ 2	21,276
Issuance of common stock, net of issuance costs (in shares)		1,995
Issuance of common stock upon exercise of stock options	50		50
Issuance of common stock upon exercise of stock option (in shares)		12
Effect of adoption of ASU 2014-09	(803)				(803)
Balance at Sep. 30, 2019	35,895	$ 15	96,559		(60,679)
Balance (in shares) at Sep. 30, 2019		15,126
Balance at Jun. 30, 2019	21,618	$ 13	74,851		(53,246)
Balance (in shares) at Jun. 30, 2019		13,120
Net loss	(7,433)				(7,433)
Share-based compensation	383		383
Issuance of common stock, net of issuance costs	21,278	$ 2	21,276
Issuance of common stock, net of issuance costs (in shares)		1,995
Issuance of common stock upon exercise of stock options	49		49
Issuance of common stock upon exercise of stock option (in shares)		11
Balance at Sep. 30, 2019	$ 35,895	$ 15	$ 96,559		$ (60,679)
Balance (in shares) at Sep. 30, 2019		15,126