Inventories (Details) (USD $)	Mar. 31, 2013	Dec. 30, 2012
Inventories [Abstract]
Raw materials	$ 21,552,000	$ 18,325,000
Work in process	33,399,000	31,525,000
Finished goods	23,151,000	22,098,000
Inventories	78,102,000	71,948,000
Inventory, noncurrent	6,100,000	6,500,000
Supplies inventory	$ 10,000,000	$ 10,200,000