SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 52,000	$ 52,000	$ 52,000
Charged to statement of income	0	0	0
Charged to other accounts	0	0	0
Deductions	10,000	0	0
Balance at end of period	42,000	52,000	52,000
Inventory Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	245,000	218,000	218,000
Charged to statement of income	119,920	221,478	256,302
Charged to other accounts	0	0	0
Deductions	170,137	194,478	256,302
Balance at end of period	$ 194,783	$ 245,000	$ 218,000