Balance Sheets - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 28,024,723	$ 30,182,115
Accounts receivable, net of allowance of $401,692 and $380,212 at 2020 and 2019, respectively	4,615,078	5,329,577
Inventories, net	3,170,140	1,847,530
Prepaid expenses and other current assets	1,390,503	1,470,922
Total current assets	37,200,444	38,830,144
Property and equipment, net	220,324	250,443
Operating lease right-of-use assets	3,790,044	4,286,064
Long-term receivables	95,483
Other assets	196,674	218,103
Total assets	41,502,969	43,584,754
Current liabilities:
Accounts payable	2,002,297	2,099,097
Accrued liabilities	2,342,197	2,721,104
Deferred revenue	5,266,715	5,092,455
Current portion of operating lease liabilities	2,255,875	2,248,189
Total current liabilities	11,867,084	12,160,845
Long-term deferred revenue	510,689	554,258
Operating lease liabilities	1,585,928	2,089,537
Other liabilities	255,517	255,517
Total liabilities	14,219,218	15,060,157
Series A - Convertible preferred stock:
Convertible preferred stock, Series A, par value $0.001; 22,918 and 23,110 shares outstanding at 2020 and 2019, respectively	5,709,027	5,758,190
Stockholders' equity:
Convertible preferred stock, Series B, par value $0.001; 10,000,000 shares authorized, 5,610,121 shares outstanding at 2020 and 2019	5,610	5,610
Common stock, par value $0.001; 300,000,000 shares authorized, 69,040,781 and 68,529,623 shares issued at 2020 and 2019, respectively	69,041	68,530
Additional paid in capital	504,990,377	504,211,040
Treasury stock, 4,015 shares at 2020 and 2019	(205,999)	(205,999)
Accumulated deficit	(483,284,305)	(481,312,774)
Total stockholders' equity	21,574,724	22,766,407
Total liabilities and stockholders' equity	$ 41,502,969	$ 43,584,754