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Product Warranty (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Product Warranties Disclosures [Abstract]      
Product Warranty Accrual $ 2,027   $ 2,074
Summary of product warranty activity      
Beginning balance 2,074 $ 2,280  
Charges to expense 741 237  
Costs incurred (788) (122)  
Ending balance $ 2,027 $ 2,395