v2.4.0.8
Capital stock (Narrative) (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
4 Months Ended 6 Months Ended 12 Months Ended
May 02, 2010
Jun. 11, 2010
Dec. 28, 2013
Dec. 29, 2012
Dec. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]          
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options     2,172,811    
Share Based Compensation Arrangement By Share Based Payment Award Expiration Period     10 years 6 years  
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights     ratably    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value     $ 4.44 $ 3.41 $ 4.36
Share-based Compensation Arrangement by Share-based Payment Award, Method of Measuring Cost of Award     Black-Scholes    
Share Based Compensation Estimated Percentage Of Options To Be Vested     85.00%    
Allocated Share-based Compensation Expense     $ 3,255 $ 2,753 $ 2,090
Tax Benefit from Stock Options Exercised     170 12 86
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms     2 years 2 months 12 days    
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Share-based Awards Other than Options     8,032    
Exercise of options     2,013 241 529
Proceeds from issuance of common shares     2,562 787 1,155
Class of Warrant or Right, Date from which Warrants or Rights Exercisable Feb. 05, 2010 Jun. 11, 2010      
Class Of Warrant Or Right Number Of Securities Called By Warrants Or Rights 250,000 600,000      
Class Of Warrant Or Right Exercise Price Of Warrants Or Rights $ 3.25 $ 5.11      
Warrants and Rights Outstanding     2,163    
Warrants And Rights Exercised     0    
Two Thousand Two Plan [Member]
         
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]          
Common Stock, Capital Shares Reserved for Future Issuance       7,500,000  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options     867,031    
Two Thousand Thirteen Stock Incentive Plan [Member]
         
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]          
Stock Incentive Plan Initiation Date     May 28, 2013    
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options     1,250,000    
Minimum [Member]
         
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]          
Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1     1 year 1 year  
Maximum [Member]
         
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]          
Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1     5 years 5 years  
Employee Share Purchase Plan Compensation Grants [Member]
         
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]          
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options     1,363,771    
Stock Issued During Period, Shares, Employee Stock Ownership Plan     80,215 111,078 119,028
Proceeds from issuance of common shares     549 546 626
Opta Minerals Inc [Member]
         
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]          
Allocated Share-based Compensation Expense     $ 485 $ 501 $ 354