Accrued payroll and employee benefits (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 28, 2012	Dec. 30, 2011
Employee Related Liabilities [Line Items]
Accrued bonuses payable	$ 33,885	$ 29,736
Accrued 401(k) contributions	6,304	6,175
Accrued vacation	8,008	7,267
Other accrued payroll and employee benefits	6,523	4,911
Total accrued payroll and employee benefits	$ 54,720	$ 48,089