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Product Warranties - Product Warranty Activity (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Guarantees [Abstract]    
Balance at the beginning of the period $ 268 $ 290
Accruals for warranties for products sold in the period 29 123
Fulfillment of warranty obligations (66) (57)
Revisions of estimated obligations 0 (10)
Balance at the end of the period $ 231 $ 346