Inventories (Details) (USD $)	Jun. 28, 2013	Dec. 31, 2012
Inventory Disclosure [Abstract]
Aluminum and steel coil	$ 66,377,000	$ 59,651,000
Raw materials	15,714,000	14,520,000
Work in process	3,172,000	1,598,000
Finished products	15,735,000	13,525,000
Inventories, net	100,998,000	89,294,000
Inventory valuation reserves	$ (2,200,000)	$ (2,900,000)