Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member] Follow-on Public Offering [Member]	Common Stock [Member]	Additional Paid-In Capital [Member] Follow-on Public Offering [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Follow-on Public Offering [Member]	Total
Balance, Value at Dec. 31, 2018		$ 39		$ 428,059	$ (294,354)	$ (114)		$ 133,630
Balance, Shares at Dec. 31, 2018		39,547,558
Stock-based compensation expense				2,234				2,234
Shares issued upon exercise of stock options, Value				234				234
Shares issued upon exercise of stock options, Shares		17,291
Shares issued for consulting services				197				197
Shares issued for consulting services, Shares		10,195
Net loss					(21,960)			(21,960)
Other comprehensive income (loss)						187		187
Balance, Value at Mar. 31, 2019		$ 39		430,724	(316,314)	73		114,522
Balance, Shares at Mar. 31, 2019		39,575,044
Balance, Value at Dec. 31, 2018		$ 39		428,059	(294,354)	(114)		133,630
Balance, Shares at Dec. 31, 2018		39,547,558
Shares issued for consulting services								197
Net loss								(77,762)
Other comprehensive income (loss)								267
Balance, Value at Sep. 30, 2019		$ 46		583,811	(372,116)	153		211,894
Balance, Shares at Sep. 30, 2019		46,673,977
Balance, Value at Mar. 31, 2019		$ 39		430,724	(316,314)	73		114,522
Balance, Shares at Mar. 31, 2019		39,575,044
Stock-based compensation expense				2,681				2,681
Shares issued upon exercise of stock options, Value		$ 1		3,974				3,975
Shares issued upon exercise of stock options, Shares		378,706
Shares issued upon vesting of restricted stock units				1,235				1,235
Shares issued upon vesting of restricted stock units, shares		74,166
Net loss					(22,960)			(22,960)
Other comprehensive income (loss)						92		92
Balance, Value at Jun. 30, 2019		$ 40		438,614	(339,274)	165		99,545
Balance, Shares at Jun. 30, 2019		40,027,916
Sale of common stock in a follow-on public offering ($23.00 per share), net of underwriting discounts and commissions and offering expenses of $8,950, value	$ 6		$ 136,519				$ 136,525
Sale of common stock in a follow-on public offering ($23.00 per share), net of underwriting discounts and commissions and offering expenses of $8,950, shares	6,325,000
Issuance of common stock upon entry into License Agreement with Enteris Biopharma, Inc. ($23.42 per share), Value				4,000				4,000
Issuance of common stock upon entry into License Agreement with Enteris Biopharma, Inc. ($23.42 per share), Shares		170,793
Stock-based compensation expense				2,835				2,835
Shares issued upon exercise of stock options, Value				1,843				1,843
Shares issued upon exercise of stock options, Shares		150,268
Net loss					(32,842)			(32,842)
Other comprehensive income (loss)						(12)		(12)
Balance, Value at Sep. 30, 2019		$ 46		583,811	(372,116)	153		211,894
Balance, Shares at Sep. 30, 2019		46,673,977
Balance, Value at Dec. 31, 2019		$ 47		587,223	(400,727)	170		186,713
Balance, Shares at Dec. 31, 2019		46,720,225
Stock-based compensation expense				2,846				2,846
Shares issued upon exercise of stock options, Value				75				75
Shares issued upon exercise of stock options, Shares		7,500
Net loss					(28,922)			(28,922)
Other comprehensive income (loss)						(238)		(238)
Balance, Value at Mar. 31, 2020		$ 47		590,144	(429,649)	(68)		160,474
Balance, Shares at Mar. 31, 2020		46,727,725
Balance, Value at Dec. 31, 2019		$ 47		587,223	(400,727)	170		186,713
Balance, Shares at Dec. 31, 2019		46,720,225
Net loss								(70,499)
Other comprehensive income (loss)								193
Balance, Value at Sep. 30, 2020		$ 47		598,663	(471,226)	363		127,847
Balance, Shares at Sep. 30, 2020		46,892,552
Balance, Value at Mar. 31, 2020		$ 47		590,144	(429,649)	(68)		160,474
Balance, Shares at Mar. 31, 2020		46,727,725
Stock-based compensation expense				2,993				2,993
Shares issued upon exercise of stock options, Value				201				201
Shares issued upon exercise of stock options, Shares		16,846
Shares issued upon vesting of restricted stock units				1,625				1,625
Shares issued upon vesting of restricted stock units, shares		119,834
Net loss					(25,068)			(25,068)
Other comprehensive income (loss)						703		703
Balance, Value at Jun. 30, 2020		$ 47		594,963	(454,717)	635		140,928
Balance, Shares at Jun. 30, 2020		46,864,405
Stock-based compensation expense				3,305				3,305
Shares issued upon exercise of stock options, Value				395				395
Shares issued upon exercise of stock options, Shares		28,147
Net loss					(16,509)			(16,509)
Other comprehensive income (loss)						(272)		(272)
Balance, Value at Sep. 30, 2020		$ 47		$ 598,663	$ (471,226)	$ 363		$ 127,847
Balance, Shares at Sep. 30, 2020		46,892,552