Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balance at beginning of period at Dec. 31, 2018	$ 170,418	$ 6	$ 693,534	$ (58)	$ (523,064)
Balance at beginning of period (in shares) at Dec. 31, 2018		59,456,493
Issuance of common stock upon exercise of stock options and incentive awards (Shares)		37,550
Issuance of common stock upon exercise of stock options and incentive awards. value	97		97
Issuance of common stock, net of $7,254 issuance costs	107,746	$ 1	107,745
Issuance of common stock, net of $7,254 issuance costs (Shares)		9,200,000
Stock-based compensation expense	2,342		2,342
Net loss	(23,075)				(23,075)
Net unrealized gain (loss) on marketable securities	103			103
Balance at end of period at Mar. 31, 2019	257,631	$ 7	803,718	45	(546,139)
Balance at end of period (in shares) at Mar. 31, 2019		68,694,043
Balance at beginning of period at Dec. 31, 2018	170,418	$ 6	693,534	(58)	(523,064)
Balance at beginning of period (in shares) at Dec. 31, 2018		59,456,493
Net loss	(73,395)
Net unrealized gain (loss) on marketable securities	235
Balance at end of period at Sep. 30, 2019	212,591	$ 7	808,866	177	(596,459)
Balance at end of period (in shares) at Sep. 30, 2019		68,701,043
Balance at beginning of period at Mar. 31, 2019	257,631	$ 7	803,718	45	(546,139)
Balance at beginning of period (in shares) at Mar. 31, 2019		68,694,043
Issuance of common stock upon exercise of stock options and incentive awards (Shares)		7,000
Issuance of common stock upon exercise of stock options and incentive awards. value	7		7
Stock-based compensation expense	2,276		2,276
Net loss	(24,038)				(24,038)
Net unrealized gain (loss) on marketable securities	183			183
Balance at end of period at Jun. 30, 2019	236,059	$ 7	806,001	228	(570,177)
Balance at end of period (in shares) at Jun. 30, 2019		68,701,043
Stock-based compensation expense	2,865		2,865
Net loss	(26,282)				(26,282)
Net unrealized gain (loss) on marketable securities	(51)			(51)
Balance at end of period at Sep. 30, 2019	212,591	$ 7	808,866	177	(596,459)
Balance at end of period (in shares) at Sep. 30, 2019		68,701,043
Balance at beginning of period at Dec. 31, 2019	186,348	$ 7	812,133	80	(625,872)
Balance at beginning of period (in shares) at Dec. 31, 2019		68,882,459
Stock-based compensation expense	1,998		1,998
Net loss	(13,088)				(13,088)
Net unrealized gain (loss) on marketable securities	(210)			(210)
Balance at end of period at Mar. 31, 2020	175,048	$ 7	814,131	(130)	(638,960)
Balance at end of period (in shares) at Mar. 31, 2020		68,882,459
Balance at beginning of period at Dec. 31, 2019	186,348	$ 7	812,133	80	(625,872)
Balance at beginning of period (in shares) at Dec. 31, 2019		68,882,459
Net loss	(35,235)
Net unrealized gain (loss) on marketable securities	2
Balance at end of period at Sep. 30, 2020	$ 156,635	$ 7	817,653	82	(661,107)
Balance at end of period (in shares) at Sep. 30, 2020	68,887,092
Balance at beginning of period at Mar. 31, 2020	$ 175,048	$ 7	814,131	(130)	(638,960)
Balance at beginning of period (in shares) at Mar. 31, 2020		68,882,459
Issuance of common stock upon exercise of stock options and incentive awards (Shares)		4,633
Issuance of common stock upon exercise of stock options and incentive awards. value	7		7
Stock-based compensation expense	963		963
Net loss	(10,726)				(10,726)
Net unrealized gain (loss) on marketable securities	316			316
Balance at end of period at Jun. 30, 2020	165,608	$ 7	815,101	186	(649,686)
Balance at end of period (in shares) at Jun. 30, 2020		68,887,092
Stock-based compensation expense	2,552		2,552
Net loss	(11,421)				(11,421)
Net unrealized gain (loss) on marketable securities	(104)			(104)
Balance at end of period at Sep. 30, 2020	$ 156,635	$ 7	$ 817,653	$ 82	$ (661,107)
Balance at end of period (in shares) at Sep. 30, 2020	68,887,092