Cash, cash equivalents and short-term investments - Additional Information (Detail)	12 Months Ended
	Dec. 28, 2012
Cash and Cash Equivalents [Line Items]
Cash equivalents and short-term investments maturity	1 month 1 day
Cash Equivalents
Cash and Cash Equivalents [Line Items]
Cash equivalents maturity	three months or less
Short-term Investments
Cash and Cash Equivalents [Line Items]
Short-term investments maturity	10 months or less