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Revenue Recognition (Narrative) (Details) - USD ($)
9 Months Ended
Sep. 30, 2020
Jun. 30, 2020
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Deferred Revenue Arrangement [Line Items]            
Deferred Revenue $ 98,300,000 $ 89,800,000 $ 81,600,000 $ 72,400,000 $ 67,700,000 $ 59,900,000
Deferred Revenue, Current 35,100,000     30,700,000    
Deferred Revenue, Noncurrent $ 63,200,000     $ 41,700,000    
Minimum            
Deferred Revenue Arrangement [Line Items]            
Extended service warranty period 12 months          
Maximum            
Deferred Revenue Arrangement [Line Items]            
Extended service warranty period 84 months