Accrued Liabilities (Details) - Warranty reserve - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Product Warranty Liability [Line Items]
Balance at beginning of year	$ 430,000	$ 405,000
Provisions	149,000	176,000
Deductions	(141,000)	(151,000)
Balance at end of year	$ 438,000	$ 430,000