Statements of Convertible Preferred Stock and Stockholders' Equity (Unaudited) - USD ($)	Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]		Total
Beginning Balance at Dec. 31, 2017	$ 5,960,475	$ 22,806	$ 450,748,403	$ (205,999)	$ (477,132,808)		$ (26,567,598)
Beginning Balance, Shares at Dec. 31, 2017	23,900	22,805,731
Issuance of common stock and warrants		$ 35,792	26,813,524				26,849,316
Issuance of common stock and warrants, Shares		35,791,927
Share-based compensation		$ 294	$ 320,150				320,444
Share-based compensation, shares		293,912
Components of net income (loss)					$ 803,025		803,025
Employee stock purchase plan		$ 41	28,615				28,656
Employee stock purchase plan, Shares		41,814
Cumulative catchup for adoption of ASC 606					$ 294,561	[1]	294,561	[1]
Ending Balance at Jun. 30, 2018	$ 5,960,475	$ 58,933	477,910,692	(205,999)	(476,035,222)		1,728,404
Ending Balance, Shares at Jun. 30, 2018	23,900	58,933,384
Beginning Balance at Mar. 31, 2018	$ 5,960,475	$ 58,901	477,872,296	(205,999)	(475,403,017)		2,322,181
Beginning Balance, Shares at Mar. 31, 2018	23,900	58,901,126
Issuance of common stock and warrants			(80,467)				(80,467)
Issuance of common stock and warrants, Shares
Share-based compensation		$ 8	103,762				103,770
Share-based compensation, shares		8,250
Components of net income (loss)					(632,205)		(632,205)
Employee stock purchase plan		$ 24	15,101				15,125
Employee stock purchase plan, Shares		24,008
Ending Balance at Jun. 30, 2018	$ 5,960,475	$ 58,933	477,910,692	(205,999)	(476,035,222)		1,728,404
Ending Balance, Shares at Jun. 30, 2018	23,900	58,933,384
Beginning Balance at Dec. 31, 2018	$ 5,960,475	$ 59,058	478,179,574	$ (205,999)	$ (476,721,490)		$ 1,311,143
Beginning Balance, Shares at Dec. 31, 2018	23,900	59,058,297
Issuance of common stock and warrants		$ 47	$ (50,479)				$ (50,432)
Issuance of common stock and warrants, Shares		46,484
Share-based compensation		$ 174	$ 954,808				$ 954,982
Share-based compensation, shares		174,462
Components of net income (loss)					$ (3,550,538)		$ (3,550,538)
Employee stock purchase plan		$ 24	$ 31,934				$ 31,958
Employee stock purchase plan, Shares		23,757
Preferred stock conversion	$ (11,522)	$ 80	$ 11,442				$ 11,522
Preferred stock conversion, shares	(45)	80,038
Ending Balance at Jun. 30, 2019	$ 5,948,953	$ 59,383	$ 479,127,279	$ (205,999)	$ (480,272,028)		$ (1,291,365)
Ending Balance, Shares at Jun. 30, 2019	23,855	59,383,038
Beginning Balance at Mar. 31, 2019	$ 5,955,354	$ 59,308	478,363,886	(205,999)	(478,844,310)		(627,115)
Beginning Balance, Shares at Mar. 31, 2019	23,880	59,308,237
Issuance of common stock and warrants		$ 14	(66,869)				(66,855)
Issuance of common stock and warrants, Shares		13,397
Share-based compensation		$ 7	807,021				807,028
Share-based compensation, shares		7,500
Components of net income (loss)					(1,427,718)		(1,427,718)
Employee stock purchase plan		$ 9	16,885				16,894
Employee stock purchase plan, Shares		9,132
Preferred stock conversion	$ (6,401)	$ 45	6,356				6,401
Preferred stock conversion, shares	(25)	44,772
Ending Balance at Jun. 30, 2019	$ 5,948,953	$ 59,383	$ 479,127,279	$ (205,999)	$ (480,272,028)		$ (1,291,365)
Ending Balance, Shares at Jun. 30, 2019	23,855	59,383,038

[1] Represents the adjustments related to the adoption of new accounting standards. See Note 2 for details.