Derivatives (Details 1)	Mar. 31, 2013 lb	Dec. 31, 2012 lb
Copper [Member]
Outstanding commodity futures contracts not designated as cash flow hedges
Notional amounts	24,400,000	22,800,000
Notional amounts	2,400,000	2,100,000
Aluminum [Member]
Outstanding commodity futures contracts not designated as cash flow hedges
Notional amounts	2,700,000	2,800,000