Restructuring charges - Charges Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2016	Jun. 28, 2015	Jun. 26, 2016	Jun. 28, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ (119)	$ 580	$ 9,849	$ 5,028
Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	(609)	(12)	9,243	3,686
Facility Closure Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	55	267	178	359
Contract Termination Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	115	261	7	901
Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	320	64	421	82
2016 Manufacturing footprint realignment plan
Restructuring Cost and Reserve [Line Items]
Restructuring charges	7		10,354
2016 Manufacturing footprint realignment plan | Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	(279)		10,068
2016 Manufacturing footprint realignment plan | Facility Closure Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0		0
2016 Manufacturing footprint realignment plan | Contract Termination Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0		0
2016 Manufacturing footprint realignment plan | Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	286		286
2015 Restructuring programs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	(247)	142	(10)	4,380
2015 Restructuring programs | Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	(442)	9	(399)	3,559
2015 Restructuring programs | Facility Closure Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	55	63	178	129
2015 Restructuring programs | Contract Termination Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	115	24	93	645
2015 Restructuring programs | Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	25	46	118	47
2014 Manufacturing footprint realignment plan
Restructuring Cost and Reserve [Line Items]
Restructuring charges	121	507	(415)	670
2014 Manufacturing footprint realignment plan | Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	112	75	(426)	212
2014 Manufacturing footprint realignment plan | Facility Closure Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	204	0	230
2014 Manufacturing footprint realignment plan | Contract Termination Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	228	0	228
2014 Manufacturing footprint realignment plan | Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 9	0	11	0
Other restructuring programs - prior years
Restructuring Cost and Reserve [Line Items]
Restructuring charges		(69)	(80)	(22)
Other restructuring programs - prior years | Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges		(96)	0	(85)
Other restructuring programs - prior years | Facility Closure Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0	0	0
Other restructuring programs - prior years | Contract Termination Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		9	(86)	28
Other restructuring programs - prior years | Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 18	$ 6	$ 35