Goodwill and other intangible assets (Details Textual)	9 Months Ended
	Sep. 23, 2012
Customer Relationships [Member] | Maximum [Member]
Goodwill and Intangible Assets (Textual) [Abstract]
Intangible assets, useful life (in years)	25 years
Customer Relationships [Member] | Minimum [Member]
Goodwill and Intangible Assets (Textual) [Abstract]
Intangible assets, useful life (in years)	4 years
Other [Member] | Maximum [Member]
Goodwill and Intangible Assets (Textual) [Abstract]
Intangible assets, useful life (in years)	21 years
Other [Member] | Minimum [Member]
Goodwill and Intangible Assets (Textual) [Abstract]
Intangible assets, useful life (in years)	3 years