Other Financial Statement Data (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Inventory write-down	$ 656,000	$ 649,000
Demonstration inventory useful life (in months)	36 months
Accumulated amortization for demonstration inventories	$ 2,400,000
Minimum
Inventory [Line Items]
Product warranties time frame, years	1 year
Maximum
Inventory [Line Items]
Product warranties time frame, years	3 years