Significant Accounting Policies (Details 1) (USD $)	12 Months Ended
	Dec. 28, 2014 item	Dec. 29, 2013 item	Dec. 30, 2012 item
Significant accounting policies
Period in arrears to consolidate operations		1 month
Number of weeks in fiscal year	52	52	53
Minimum
Significant accounting policies
Amortization term of equipment incentives	2 years
Maximum
Significant accounting policies
Amortization term of equipment incentives	3 years
International
Significant accounting policies
Incremental change in revenues due to change in consolidation policy		2,100,000
Incremental change in loss before income taxes due to change in consolidation policy		215,000