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Sales, Contract Assets and Contract Liabilities (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2020
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Sales, Contract Assets and Contract Liabilities                    
Revenue $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0
Cost of goods sold before warranty adjustment                 450,000  
Cost of goods sold - warranty adjustment                 171,000 1,000
Contract assets 92,000       39,000       92,000 39,000
Contract liabilities $ 94,000       $ 50,000       $ 94,000 $ 50,000