Schedule of Valuation and Qualifying Accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts
Balance at beginning of year	$ 150,000	$ 150,000
Charges to statement of income	6,435	1,566
Write-offs	(16,435)	(1,566)
Balance at end of year	140,000	150,000
Inventory Valuation Reserve
Balance at beginning of year	562,000	577,000
Charges to statement of income	75,023	80,793
Write-offs	(73,023)	(95,793)
Balance at end of year	$ 564,000	$ 562,000