STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance at Dec. 31, 2016	$ 22,194	$ 9	$ 134,715	$ (19)	$ (112,511)
Beginning Balance, shares at Dec. 31, 2016		9,082,366
Issuance of common stock for cash, net of offering costs	69		69
Issuance of common stock for cash, net of offering costs, shares		85,068
Issuance of common stock upon vesting of Restricted Stock Units, value	0	$ 0	0	0	0
Issuance of common stock upon vesting of Restricted Stock Units, shares		5,434
Share-based compensation	101		101
Change in unrealized loss on marketable securities	10			10
Net loss	(4,338)				(4,338)
Ending Balance at Mar. 31, 2017	18,036	$ 9	134,885	(9)	(116,849)
Ending Balance, shares at Mar. 31, 2017		9,172,868
Beginning Balance at Dec. 31, 2016	22,194	$ 9	134,715	(19)	(112,511)
Beginning Balance, shares at Dec. 31, 2016		9,082,366
Change in unrealized loss on marketable securities	16
Net loss	(14,293)
Ending Balance at Sep. 30, 2017	14,352	$ 12	141,147	(3)	(126,804)
Ending Balance, shares at Sep. 30, 2017		11,750,744
Beginning Balance at Mar. 31, 2017	18,036	$ 9	134,885	(9)	(116,849)
Beginning Balance, shares at Mar. 31, 2017		9,172,868
Issuance of common stock for cash, net of offering costs	2,110	$ 1	2,109
Issuance of common stock for cash, net of offering costs, shares		934,214
Issuance of common stock upon vesting of Restricted Stock Units, value	0	$ 0	0	0	0
Issuance of common stock upon vesting of Restricted Stock Units, shares		9,504
Share-based compensation	119		119
Change in unrealized loss on marketable securities	4			4
Net loss	(5,522)				(5,522)
Ending Balance at Jun. 30, 2017	14,747	$ 10	137,113	(5)	(122,371)
Ending Balance, shares at Jun. 30, 2017		10,116,586
Issuance of common stock for cash, net of offering costs	3,917	$ 2	3,915
Issuance of common stock for cash, net of offering costs, shares		1,634,158
Share-based compensation	119		119
Change in unrealized loss on marketable securities	2			2
Net loss	(4,433)				(4,433)
Ending Balance at Sep. 30, 2017	14,352	$ 12	141,147	(3)	(126,804)
Ending Balance, shares at Sep. 30, 2017		11,750,744
Issuance of common stock for cash, net of offering costs, shares		24,085
Issuance of common stock upon vesting of Restricted Stock Units, value	0	$ 0	0	0	0
Issuance of common stock upon vesting of Restricted Stock Units, shares		233
Share-based compensation	119		119
Change in unrealized loss on marketable securities	1			1
Net loss	(4,197)				(4,197)
Ending Balance at Dec. 31, 2017	$ 10,275	$ 12	141,266	(2)	(131,001)
Ending Balance, shares at Dec. 31, 2017	11,775,062	11,775,062
Issuance of common stock for cash, net of offering costs	$ 3,415	$ 2	3,413
Issuance of common stock for cash, net of offering costs, shares		2,133,828
Issuance of common stock upon vesting of Restricted Stock Units, value	0	$ 0	0	0	0
Issuance of common stock upon vesting of Restricted Stock Units, shares		5,430
Share-based compensation	97		97
Change in unrealized loss on marketable securities	2			2
Net loss	(2,735)				(2,735)
Ending Balance at Mar. 31, 2018	11,054	$ 14	144,776		(133,736)
Ending Balance, shares at Mar. 31, 2018		13,914,320
Beginning Balance at Dec. 31, 2017	$ 10,275	$ 12	141,266	(2)	(131,001)
Beginning Balance, shares at Dec. 31, 2017	11,775,062	11,775,062
Change in unrealized loss on marketable securities	$ 2
Net loss	(6,444)
Ending Balance at Sep. 30, 2018	$ 7,463	$ 14	144,894		(137,445)
Ending Balance, shares at Sep. 30, 2018	13,923,825	13,923,825
Beginning Balance at Mar. 31, 2018	$ 11,054	$ 14	144,776		(133,736)
Beginning Balance, shares at Mar. 31, 2018		13,914,320
Issuance of common stock upon vesting of Restricted Stock Units, value	0	$ 0	0	$ 0	0
Issuance of common stock upon vesting of Restricted Stock Units, shares		9,505
Share-based compensation	60		60
Net loss	(2,116)				(2,116)
Ending Balance at Jun. 30, 2018	8,998	$ 14	144,836		(135,852)
Ending Balance, shares at Jun. 30, 2018		13,923,825
Share-based compensation	58		58
Net loss	(1,593)				(1,593)
Ending Balance at Sep. 30, 2018	$ 7,463	$ 14	$ 144,894		$ (137,445)
Ending Balance, shares at Sep. 30, 2018	13,923,825	13,923,825