Intangible assets, net (Details) (USD $)	9 Months Ended
	Sep. 27, 2013	Sep. 28, 2012	Dec. 28, 2012
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization (definite lives)	$ 5,300,000		$ 5,300,000
Accumulated amortization	(5,183,000)		(4,833,000)
Net intangible assets subject to amortization	117,000		467,000
Indefinite-lived Intangible Assets [Line Items]
Intangible assets, net	2,717,000		3,067,000
Weighted average life of finite intangible assets	1 year
Amortization expense for period	400,000	400,000
Tradename [Member]
Indefinite-lived Intangible Assets [Line Items]
Intangible assets not subject to amortization (indefinite lives)	2,600,000		2,600,000
Customer relationships [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization (definite lives)	3,300,000		3,300,000
Accumulated amortization	(3,183,000)		(2,833,000)
Technology [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization (definite lives)	2,000,000		2,000,000
Accumulated amortization	$ (2,000,000)		$ (2,000,000)