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, 2017		$ 33		$ 307,158	$ (220,341)	$ (70)		$ 86,780
Balance, Shares at Dec. 31, 2017		32,662,255
Stock-based compensation expense				1,871				1,871
Shares issued upon exercise of stock options, Value				263				263
Shares issued upon exercise of stock options, Shares		37,688
Net loss					(16,767)			(16,767)
Other comprehensive income (loss)						(44)		(44)
Balance, Value at Mar. 31, 2018		$ 33		309,292	(237,108)	(114)		72,103
Balance, Shares at Mar. 31, 2018		32,699,943
Balance, Value at Dec. 31, 2017		$ 33		307,158	(220,341)	(70)		86,780
Balance, Shares at Dec. 31, 2017		32,662,255
Net loss								(53,361)
Other comprehensive income (loss)								83
Balance, Value at Sep. 30, 2018		$ 39		423,180	(273,702)	13		149,530
Balance, Shares at Sep. 30, 2018		39,389,515
Balance, Value at Mar. 31, 2018		$ 33		309,292	(237,108)	(114)		72,103
Balance, Shares at Mar. 31, 2018		32,699,943
Sale of common stock under license agreement, Value		$ 1		14,555				14,556
Sale of common stock under license agreement, Shares		1,174,827
Stock-based compensation expense				2,069				2,069
Shares issued upon exercise of stock options, Value				1,485				1,485
Shares issued upon exercise of stock options, Shares		184,444
Net loss					(17,194)			(17,194)
Other comprehensive income (loss)						57		57
Balance, Value at Jun. 30, 2018		$ 34		327,401	(254,302)	(57)		73,076
Balance, Shares at Jun. 30, 2018		34,059,214
Sale of common stock, net of underwriting discounts and commissions and offering expenses, value	$ 5		$ 92,072				$ 92,077
Sale of common, net of underwriting discounts and commissions and offering expenses, shares	5,175,000
Stock-based compensation expense				1,819				1,819
Shares issued upon exercise of stock options, Value				1,888				1,888
Shares issued upon exercise of stock options, Shares		155,301
Net loss					(19,400)			(19,400)
Other comprehensive income (loss)						70		70
Balance, Value at Sep. 30, 2018		$ 39		423,180	(273,702)	13		149,530
Balance, Shares at Sep. 30, 2018		39,389,515
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 under license agreement, Value				4,000				4,000
Sale of common stock under license agreement, Shares		170,793
Sale of common stock, net of underwriting discounts and commissions and offering expenses, value	$ 6		$ 136,519				$ 136,525
Sale of common, net of underwriting discounts and commissions and offering expenses, shares	6,325,000
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