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, 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	31,986	$ 5	31,981
Issuance of common stock for public offering, net of issuance costs, 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	7
Net loss	(21,301)
Balance at Jun. 30, 2020	108,961	$ 22	388,719	41	(279,821)
Balance (in shares) at Jun. 30, 2020		22,050,745
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	27,955	$ 5	27,950
Issuance of common stock for public offering, net of issuance costs, 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
Balance at Dec. 31, 2020	76,069	$ 22	390,803	5	(314,761)
Balance (in shares) at Dec. 31, 2020		22,097,820
Stock-based compensation expense	1,026		1,026
Stock-based compensation expense		10,149
Issuance of common stock from stock grants and option exercises	182		182
Issuance of common stock from stock grants and option exercises, shares		38,058
Issuance of common stock for public offering, net of issuance costs	49,250	$ 9	49,241
Issuance of common stock for public offering, net of issuance costs, shares		9,185,000
Net loss	(22,438)				(22,438)
Balance at Mar. 31, 2021	104,089	$ 31	441,252	5	(337,199)
Balance (in shares) at Mar. 31, 2021		31,331,027
Balance at Dec. 31, 2020	76,069	$ 22	390,803	5	(314,761)
Balance (in shares) at Dec. 31, 2020		22,097,820
Unrealized (loss) gain on available-for-sale debt securities	(3)
Net loss	(42,366)
Balance at Jun. 30, 2021	85,164	$ 31	442,258	2	(357,127)
Balance (in shares) at Jun. 30, 2021		31,349,740
Balance at Mar. 31, 2021	104,089	$ 31	441,252	5	(337,199)
Balance (in shares) at Mar. 31, 2021		31,331,027
Stock-based compensation expense	983		983
Stock-based compensation expense		13,713
Issuance of common stock from stock grants and option exercises	23		23
Issuance of common stock from stock grants and option exercises, shares		5,000
Unrealized (loss) gain on available-for-sale debt securities	(3)			(3)
Net loss	(19,928)				(19,928)
Balance at Jun. 30, 2021	$ 85,164	$ 31	$ 442,258	$ 2	$ (357,127)
Balance (in shares) at Jun. 30, 2021		31,349,740