Effect of Recording Equity-Based Compensation (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	$ 852	$ 1,148	$ 2,454	$ 3,012
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	213	350	563	808
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	309	731	945	1,943
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	$ 330	$ 67	$ 946	$ 261