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Summary of Significant Accounting Policies - Product Warranty (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Summary of product warranty activity    
Beginning balance $ 2,194 $ 1,916
Charges to expense 1,091 2,186
Costs incurred (1,473) (1,908)
Ending balance $ 1,812 $ 2,194