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Summary of Significant Accounting Policies - Changes in Product Warranty Accrual (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 29, 2018
Sep. 30, 2017
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]    
Warranty accrual, beginning of period $ 1,149 $ 910
Accrual for warranties issued 943 712
Changes to pre-existing warranties (including changes in estimates) 779 (116)
Settlements made (974) (486)
Warranty accrual, end of period $ 1,897 $ 1,020