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Summary of Significant Accounting Policies - Changes in Product Warranty Accrual (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2017
Oct. 01, 2016
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]    
Warranty accrual, beginning of period $ 910 $ 1,222
Accrual for warranties issued 712 722
Changes to pre-existing warranties (including changes in estimates) (116) 99
Settlements made (486) (751)
Warranty accrual, end of period $ 1,020 $ 1,292