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Other Financial Statement Data (Narrative) (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Inventory [Line Items]          
Demonstration inventory useful life (in months)     36 months    
Accumulated amortization for demonstration inventories $ 2,600,000   $ 2,600,000   $ 2,700,000
Amortization expense related to demonstration inventories $ 168,000 $ 211,000 $ 322,000 $ 442,000  
Minimum          
Inventory [Line Items]          
Product warranties time frame, years     1 year    
Maximum          
Inventory [Line Items]          
Product warranties time frame, years     3 years