Statements of Shareholders' Equity - USD ($)	Total	May 2016 Offering [Member]	October 2016 Offering [Member]	March 2017 Registered Direct Offering [Member]	August 2017 Private Placement [Member]	December 2017 Registered Direct Offering [Member]	Common Stock [Member]	Common Stock [Member] May 2016 Offering [Member]	Common Stock [Member] October 2016 Offering [Member]	Common Stock [Member] March 2017 Registered Direct Offering [Member]	Common Stock [Member] August 2017 Private Placement [Member]	Common Stock [Member] December 2017 Registered Direct Offering [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] May 2016 Offering [Member]	Additional Paid-in Capital [Member] October 2016 Offering [Member]	Additional Paid-in Capital [Member] March 2017 Registered Direct Offering [Member]	Additional Paid-in Capital [Member] August 2017 Private Placement [Member]	Additional Paid-in Capital [Member] December 2017 Registered Direct Offering [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2015	$ 3,692,735						$ 656						$ 158,928,627						$ (155,236,548)
Beginning balance, shares at Dec. 31, 2015							6,556,685
Net loss	(4,875,198)
Ending balance at Mar. 31, 2016	(489,231)
Beginning balance at Dec. 31, 2015	3,692,735						$ 656						158,928,627						(155,236,548)
Beginning balance, shares at Dec. 31, 2015							6,556,685
Stock-based compensation expense	1,593,947												1,593,947
Shares issued for restricted stock units							$ 1						(1)
Shares issued for restricted stock units, shares							4,449
Shares and warrants issued, net of issuance costs	1,400,000	$ 4,333,283	$ 8,972,725					$ 166	$ 910					$ 4,333,117	$ 8,971,815
Shares and warrants issued, net of issuance costs, shares								1,662,191	9,100,000
Shares issued pursuant to stock purchase agreement, net of issuance costs	465,293						$ 17						465,276
Shares issued pursuant to stock purchase agreement, net of issuance costs, shares							173,145
Fractional shares issued upon one-for-three reverse stock split, shares							2,927
Net loss	(18,399,322)																		(18,399,322)
Ending balance at Dec. 31, 2016	658,661						$ 1,750						174,292,781						(173,635,870)
Ending balance, shares at Dec. 31, 2016							17,499,397
Beginning balance at Mar. 31, 2016	(489,231)
Net loss	(4,594,174)
Ending balance at Jun. 30, 2016	(419,402)
Net loss	(4,743,076)
Ending balance at Sep. 30, 2016	(4,556,158)
Net loss	(4,186,874)
Ending balance at Dec. 31, 2016	658,661						$ 1,750						174,292,781						(173,635,870)
Ending balance, shares at Dec. 31, 2016							17,499,397
Net loss	(4,432,707)
Ending balance at Mar. 31, 2017	10,418,069
Beginning balance at Dec. 31, 2016	658,661						$ 1,750						174,292,781						(173,635,870)
Beginning balance, shares at Dec. 31, 2016							17,499,397
Stock-based compensation expense	1,247,481												1,247,481
Shares issued for restricted stock units							$ 16						(16)
Shares issued for restricted stock units, shares							155,829
Shares issued upon exercise of common stock warrants	7,498,535						$ 682						7,497,853
Shares issued upon exercise of common stock warrants, shares							6,816,850
Shares and warrants issued, net of issuance costs				$ 8,559,959	$ 2,023,939	$ 2,921,196				$ 432	$ 146	$ 492				$ 8,559,527	$ 2,023,793	$ 2,920,704
Shares and warrants issued, net of issuance costs, shares										4,320,000	1,466,667	4,925,000
Net loss	(21,613,737)																		(21,613,737)
Ending balance at Dec. 31, 2017	1,296,034						$ 3,518						196,542,123						(195,249,607)
Ending balance, shares at Dec. 31, 2017							35,183,743
Beginning balance at Mar. 31, 2017	10,418,069
Net loss	(5,693,151)
Ending balance at Jun. 30, 2017	7,342,257
Net loss	(5,821,306)
Ending balance at Sep. 30, 2017	4,026,079
Net loss	(5,666,573)
Ending balance at Dec. 31, 2017	$ 1,296,034						$ 3,518						$ 196,542,123						$ (195,249,607)
Ending balance, shares at Dec. 31, 2017							35,183,743