Condensed Statement of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		1,973,039
Beginning balance at Dec. 31, 2017	$ 7,048	$ 0	$ 232,922	$ (225,874)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	139		139
Net loss	(8,206)			(8,206)
Beginning balance (in shares) at Mar. 31, 2018		1,973,039
Beginning balance at Mar. 31, 2018	(1,019)	$ 0	233,061	(234,080)	0
Beginning balance (in shares) at Dec. 31, 2017		1,973,039
Beginning balance at Dec. 31, 2017	7,048	$ 0	232,922	(225,874)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized loss on marketable securities	0
Net loss	(17,042)
Beginning balance (in shares) at Jun. 30, 2018		11,973,039
Beginning balance at Jun. 30, 2018	36,080	$ 1	278,995	(242,916)	0
Beginning balance (in shares) at Mar. 31, 2018		1,973,039
Beginning balance at Mar. 31, 2018	(1,019)	$ 0	233,061	(234,080)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with public offering (in shares)		10,000,000
Issuance of common stock in connection with public offering	45,605	$ 1	45,604
Stock-based compensation	330		330
Unrealized loss on marketable securities	0
Net loss	(8,836)			(8,836)
Beginning balance (in shares) at Jun. 30, 2018		11,973,039
Beginning balance at Jun. 30, 2018	$ 36,080	$ 1	278,995	(242,916)	0
Beginning balance (in shares) at Dec. 31, 2018	11,973,039	11,973,039
Beginning balance at Dec. 31, 2018	$ 18,710	$ 1	279,946	(261,232)	(5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	361		361
Unrealized loss on marketable securities	6				6
Net loss	(9,426)			(9,426)
Beginning balance (in shares) at Mar. 31, 2019		11,973,039
Beginning balance at Mar. 31, 2019	$ 9,651	$ 1	280,307	(270,658)	1
Beginning balance (in shares) at Dec. 31, 2018	11,973,039	11,973,039
Beginning balance at Dec. 31, 2018	$ 18,710	$ 1	279,946	(261,232)	(5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized loss on marketable securities	5
Net loss	$ (18,786)
Beginning balance (in shares) at Jun. 30, 2019	17,723,039	17,723,039.000
Beginning balance at Jun. 30, 2019	$ 19,007	$ 2	299,023	(280,018)	0
Beginning balance (in shares) at Mar. 31, 2019		11,973,039
Beginning balance at Mar. 31, 2019	9,651	$ 1	280,307	(270,658)	1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with public offering (in shares)		5,750,000
Issuance of common stock in connection with public offering	18,331	$ 1	18,330
Stock-based compensation	386		386
Unrealized loss on marketable securities	(1)				(1)
Net loss	$ (9,360)			(9,360)
Beginning balance (in shares) at Jun. 30, 2019	17,723,039	17,723,039.000
Beginning balance at Jun. 30, 2019	$ 19,007	$ 2	$ 299,023	$ (280,018)	$ 0