Income taxes - Reconciliation of Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 28, 2014	Dec. 29, 2013
Income Tax Disclosure [Abstract]
U.S. statutory tax rate	35.00%	35.00%	35.00%
Increase (decrease) in taxes resulting from:
State taxes (net of federal income tax benefit)	3.20%	2.40%	10.80%
Effect of foreign operations	0.50%	0.10%	1.50%
Domestic Manufacturing Deduction	(2.00%)	(1.60%)	(3.30%)
Uncertain tax positions, settlements and lapse of statutes of limitations	(0.20%)	(0.30%)	(40.30%)
Net deferred tax write offs and deferred tax rate adjustments	(1.60%)	(0.30%)	(4.30%)
Non-deductible transactions costs	0.50%	0.70%	13.50%
Loss on sale of subsidiary	0.00%	(12.60%)	0.00%
Non-deductible goodwill	0.40%	3.00%	0.00%
Tax provision and state refund adjustments	0.00%	0.00%	12.50%
Other, net	0.30%	(1.00%)	(0.90%)
Effective tax rate	36.10%	25.40%	24.50%