Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	At-the-market Sale Agreement [Member]	Public Offering [Member]	Common Stock [Member]	Common Stock [Member] At-the-market Sale Agreement [Member]	Common Stock [Member] Public Offering [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] At-the-market Sale Agreement [Member]	Additional Paid-in Capital [Member] Public Offering [Member]	Accumulated Other Comprehensive Income [Member]	Treasury stock [Member]	Accumulated deficit [Member]
Balance at Dec. 31, 2018	$ 42,911			$ 360			$ 129,825				$ (1,129)	$ (86,145)
Balance, shares at Dec. 31, 2018				35,860,114							(91,423)
Exercise of stock options	25						25
Exercise of stock options, shares				25,000
Issuance of stock		$ 455			$ 1			$ 454
Issuance of stock, shares					35,362
Issuance of warrants	421						421
Vesting of restricted stock units	(121)										$ (121)
Vesting of restricted stock units, shares				25,132							(10,467)
Stock-based compensation expense	2,658						2,658
Change in unrealized gain (loss) on investments	1									$ 1
Net loss	(11,917)											(11,917)
Balance at Mar. 31, 2019	34,433			$ 361			133,383			1	$ (1,250)	(98,062)
Balance, shares at Mar. 31, 2019				35,945,608							(101,890)
Balance at Dec. 31, 2018	42,911			$ 360			129,825				$ (1,129)	(86,145)
Balance, shares at Dec. 31, 2018				35,860,114							(91,423)
Change in unrealized gain (loss) on investments	24
Net loss	(26,366)
Balance at Jun. 30, 2019	55,224			$ 402			168,848			24	$ (1,539)	(112,511)
Balance, shares at Jun. 30, 2019				39,914,668							(128,697)
Balance at Mar. 31, 2019	34,433			$ 361			133,383			1	$ (1,250)	(98,062)
Balance, shares at Mar. 31, 2019				35,945,608							(101,890)
Exercise of stock options	90						90
Exercise of stock options, shares				36,790
Issuance of stock, shares						3,833,334
Issuance of common stock upon exercise of warrants							178				$ (178)
Issuance of common stock upon exercise of warrants, shares				44,814							(14,893)
Vesting of restricted stock units	(111)			$ 3			(3)				$ (111)
Vesting of restricted stock units, shares				54,122							(11,914)
Issuance of stock			$ 32,222			$ 38			$ 32,184
Stock-based compensation expense	3,016						3,016
Change in unrealized gain (loss) on investments	23									23
Net loss	(14,449)											(14,449)
Balance at Jun. 30, 2019	55,224			$ 402			168,848			24	$ (1,539)	(112,511)
Balance, shares at Jun. 30, 2019				39,914,668							(128,697)
Balance at Dec. 31, 2019	$ 36,213			$ 402			174,515			18	$ (1,703)	(137,019)
Balance, shares at Dec. 31, 2019	40,030,763			40,030,763							(155,706)
Exercise of stock options	$ 64						64
Exercise of stock options, shares				10,636
Vesting of restricted stock units	(116)			$ 1			(1)				$ (116)
Vesting of restricted stock units, shares				84,055							(34,874)
Stock-based compensation expense	3,995						3,995
Change in unrealized gain (loss) on investments	47									47
Net loss	(13,946)											(13,946)
Balance at Mar. 31, 2020	26,257			$ 403			178,573			65	$ (1,819)	(150,965)
Balance, shares at Mar. 31, 2020				40,125,454							(190,580)
Balance at Dec. 31, 2019	$ 36,213			$ 402			174,515			18	$ (1,703)	(137,019)
Balance, shares at Dec. 31, 2019	40,030,763			40,030,763							(155,706)
Exercise of stock options, shares	10,636
Issuance of warrants	$ 400
Change in unrealized gain (loss) on investments	(5)
Net loss	(21,833)
Balance at Jun. 30, 2020	$ 20,291			$ 403			180,549			13	$ (1,822)	(158,852)
Balance, shares at Jun. 30, 2020	40,135,290			40,135,290							(191,616)
Balance at Mar. 31, 2020	$ 26,257			$ 403			178,573			65	$ (1,819)	(150,965)
Balance, shares at Mar. 31, 2020				40,125,454							(190,580)
Vesting of restricted stock units	(3)										$ (3)
Vesting of restricted stock units, shares				9,836							(1,036)
Stock-based compensation expense	1,976						1,976
Change in unrealized gain (loss) on investments	(52)									(52)
Net loss	(7,887)											(7,887)
Balance at Jun. 30, 2020	$ 20,291			$ 403			$ 180,549			$ 13	$ (1,822)	$ (158,852)
Balance, shares at Jun. 30, 2020	40,135,290			40,135,290							(191,616)