v2.4.0.8
Goodwill and intangible assets (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended 9 Months Ended 12 Months Ended
Dec. 28, 2013
Dec. 29, 2012
Dec. 31, 2011
Sep. 30, 2013
Opta Minerals Inc [Member]
Dec. 28, 2013
Opta Minerals Inc [Member]
Goodwill [Line Items]          
Goodwill, Impairment Loss $ 3,552 $ 0 $ 0   $ 3,552
Projected long-term annual operating income growth       2.50%  
Fair Value Inputs Discount Rate       14.00%  
Estimated cumulative average operating income growth       25.70%