Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2018	$ 119,945	$ 12	$ 323,279	$ (4)	$ (203,342)
Balance (in shares) at Dec. 31, 2018		11,954,528
Stock-based compensation expense	829		829
Issuance of common stock from stock grants and option exercises	106		106
Issuance of common stock from stock grants and option exercises, shares		19,576
Unrealized (loss) gain on available-for-sale debt securities	17			17
Net loss	(15,082)				(15,082)
Balance at Mar. 31, 2019	105,815	$ 12	324,214	13	(218,424)
Balance (in shares) at Mar. 31, 2019		11,974,104
Balance at Dec. 31, 2018	119,945	$ 12	323,279	(4)	(203,342)
Balance (in shares) at Dec. 31, 2018		11,954,528
Unrealized (loss) gain on available-for-sale debt securities	35
Net loss	(41,568)
Balance at Sep. 30, 2019	81,272	$ 12	326,139	31	(244,910)
Balance (in shares) at Sep. 30, 2019		12,029,992
Balance at Mar. 31, 2019	105,815	$ 12	324,214	13	(218,424)
Balance (in shares) at Mar. 31, 2019		11,974,104
Stock-based compensation expense	903		903
Stock-based compensation expense		5,999
Issuance of common stock from stock grants and option exercises	129		129
Issuance of common stock from stock grants and option exercises, shares		28,425
Unrealized (loss) gain on available-for-sale debt securities	44			44
Net loss	(13,780)				(13,780)
Balance at Jun. 30, 2019	93,111	$ 12	325,246	57	(232,204)
Balance (in shares) at Jun. 30, 2019		12,008,528
Stock-based compensation expense	801		801
Stock-based compensation expense		7,393
Issuance of common stock from stock grants and option exercises	92		92
Issuance of common stock from stock grants and option exercises, shares		14,071
Unrealized (loss) gain on available-for-sale debt securities	(26)			(26)
Net loss	(12,706)				(12,706)
Balance at Sep. 30, 2019	81,272	$ 12	326,139	31	(244,910)
Balance (in shares) at Sep. 30, 2019		12,029,992
Balance at Dec. 31, 2019	68,336	$ 12	326,810	34	(258,520)
Balance (in shares) at Dec. 31, 2019		12,040,835
Stock-based compensation expense	805		805
Stock-based compensation expense		7,817
Issuance of common stock from stock grants and option exercises	339		339
Issuance of common stock from stock grants and option exercises, shares		62,969
Issuance of common stock for public offering, net of issuance costs of $2,514 and $ [ ]	31,986	$ 5	31,981
Issuance of common stock for public offering, net of issuance costs of $2,514, shares		5,307,692
Unrealized (loss) gain on available-for-sale debt securities	106			106
Net loss	(4,053)				(4,053)
Balance at Mar. 31, 2020	97,519	$ 17	359,935	140	(262,573)
Balance (in shares) at Mar. 31, 2020		17,419,313
Balance at Dec. 31, 2019	68,336	$ 12	326,810	34	(258,520)
Balance (in shares) at Dec. 31, 2019		12,040,835
Unrealized (loss) gain on available-for-sale debt securities	(26)
Net loss	(37,334)
Balance at Sep. 30, 2020	94,059	$ 22	389,883	8	(295,854)
Balance (in shares) at Sep. 30, 2020		22,082,924
Balance at Mar. 31, 2020	97,519	$ 17	359,935	140	(262,573)
Balance (in shares) at Mar. 31, 2020		17,419,313
Stock-based compensation expense	834		834
Stock-based compensation expense		16,048
Issuance of common stock for public offering, net of issuance costs of $2,514 and $ [ ]	27,955	$ 5	27,950
Issuance of common stock for public offering, net of issuance costs of $2,514, shares		4,615,384
Unrealized (loss) gain on available-for-sale debt securities	(99)			(99)
Net loss	(17,248)				(17,248)
Balance at Jun. 30, 2020	108,961	$ 22	388,719	41	(279,821)
Balance (in shares) at Jun. 30, 2020		22,050,745
Stock-based compensation expense	1,068		1,068
Stock-based compensation expense		12,295
Issuance of common stock from stock grants and option exercises	96		96
Issuance of common stock from stock grants and option exercises, shares		19,884
Unrealized (loss) gain on available-for-sale debt securities	(33)			(33)
Net loss	(16,033)				(16,033)
Balance at Sep. 30, 2020	$ 94,059	$ 22	$ 389,883	$ 8	$ (295,854)
Balance (in shares) at Sep. 30, 2020		22,082,924