Schedule of Valuation and Qualifying Accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Allowance, Credit Loss
Balance at beginning of year	$ 140,000	$ 150,000
Charges to statement of income	0	6,435
Write-offs	0	(16,435)
Balance at end of year	140,000	140,000
SEC Schedule, 12-09, Reserve, Inventory
Balance at beginning of year	564,000	562,000
Charges to statement of income	17,870	75,023
Write-offs	(2,870)	(73,023)
Balance at end of year	$ 579,000	$ 564,000