Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Public Offering [Member]	ATM Facility [Member]	Common Stock [Member]	Common Stock [Member] Public Offering [Member]	Common Stock [Member] ATM Facility [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Public Offering [Member]	Additional Paid-in Capital [Member] ATM Facility [Member]	Retained Earnings [Member]
Beginning balance at Dec. 31, 2019	$ 186,013			$ 3			$ 330,714			$ (144,704)
Beginning balance, shares at Dec. 31, 2019				31,643,000
Stock-based compensation expense	6,721						6,721
Exercise of stock options	96						96
Exercise of stock options, shares				32,000
Vesting of restricted stock awards and units, shares				21,000
Issuance of common stock, net of offering costs		$ 93,628	$ 8,130		$ 1			$ 93,627	$ 8,130
Issuance of common stock upon public offering, net of offering costs, shares					4,350,000	384,000
Issuance of common stock under the 2018 employee stock purchase plan, shares				2,000
Net loss	(54,801)									(54,801)
Ending balance at Jun. 30, 2020	239,787			$ 4			439,288			(199,505)
Ending balance, shares at Jun. 30, 2020				36,432,000
Beginning balance at Mar. 31, 2020	256,525			$ 4			427,198			(170,677)
Beginning balance, shares at Mar. 31, 2020				36,011,000
Stock-based compensation expense	3,899						3,899
Exercise of stock options	61						61
Exercise of stock options, shares				25,000
Vesting of restricted stock awards and units, shares				10,000
Issuance of common stock, net of offering costs			8,130						8,130
Issuance of common stock upon public offering, net of offering costs, shares						384,000
Issuance of common stock under the 2018 employee stock purchase plan, shares				2,000
Net loss	(28,828)									(28,828)
Ending balance at Jun. 30, 2020	239,787			$ 4			439,288			(199,505)
Ending balance, shares at Jun. 30, 2020				36,432,000
Beginning balance at Dec. 31, 2020	254,344			$ 4			518,756			(264,416)
Beginning balance, shares at Dec. 31, 2020				41,569,000
Stock-based compensation expense	9,326						9,326
Exercise of stock options	$ 850						850
Exercise of stock options, shares	196,872			197,000
Issuance of common stock, net of offering costs			14,550						14,550
Issuance of common stock upon public offering, net of offering costs, shares						1,829,000
Issuance of common stock under the 2018 employee stock purchase plan	$ 208						208
Issuance of common stock under the 2018 employee stock purchase plan, shares				28,000
Net loss	(58,286)									(58,286)
Ending balance at Jun. 30, 2021	220,992			$ 4			543,690			(322,702)
Ending balance, shares at Jun. 30, 2021				43,623,000
Beginning balance at Mar. 31, 2021	232,930			$ 4			524,241			(291,315)
Beginning balance, shares at Mar. 31, 2021				41,766,000
Stock-based compensation expense	4,691						4,691
Issuance of common stock, net of offering costs			$ 14,550						$ 14,550
Issuance of common stock upon public offering, net of offering costs, shares						1,829,000
Issuance of common stock under the 2018 employee stock purchase plan	208						208
Issuance of common stock under the 2018 employee stock purchase plan, shares				28,000
Net loss	(31,387)									(31,387)
Ending balance at Jun. 30, 2021	$ 220,992			$ 4			$ 543,690			$ (322,702)
Ending balance, shares at Jun. 30, 2021				43,623,000