Inventories (Details) (USD $)	Mar. 29, 2013	Dec. 31, 2012
Inventory Disclosure [Abstract]
Aluminum and steel coil	$ 69,760,000	$ 59,651,000
Raw materials	15,473,000	14,520,000
Work in process	2,669,000	1,598,000
Finished products	16,505,000	13,525,000
Inventories, net	104,407,000	89,294,000
Inventory valuation reserves	$ (2,800,000)	$ (2,900,000)