Derivative Financial Instruments (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Fair values of derivative instruments, balance sheet
Commodity futures, asset derivatives (in dollars)	$ 982,000		$ 982,000		$ 1,010,000
Commodity futures, liability derivatives (in dollars)	(3,581,000)		(3,581,000)		4,487,000
Gains or losses on derivative instruments, statement of income
Ineffectiveness - amount of gain (loss) recognized in income on related hedged items	160,000	(108,000)	456,000	113,000
Gain (loss) excluded from hedge effectiveness testing	(599,000)	(1,200,000)	(782,000)	1,100,000
Other Current Assets [Member]
Fair values of derivative instruments, balance sheet
Fair value of derivatives including required margin deposits	5,100,000		5,100,000		3,600,000
Designated As Hedging Instrument [Member]
Gains or losses on derivative instruments, statement of income
Amount of gain (loss) recognized in income on related hedged items	2,193,000	(717,000)	689,000	(6,209,000)
Future [Member] | Aluminum Commodity [Member] | Long [Member]
Commodity contract commitments
Commodity contract (in MT/Lbs)			3,550
Future [Member] | Aluminum Commodity [Member] | Short [Member]
Commodity contract commitments
Commodity contract (in MT/Lbs)			3,575
Future [Member] | Copper Commodity [Member] | Long [Member]
Commodity contract commitments
Commodity contract (in MT/Lbs)			7,129
Future [Member] | Copper Commodity [Member] | Short [Member]
Commodity contract commitments
Commodity contract (in MT/Lbs)			21,636
Future [Member] | Silver Commodity [Member] | Short [Member]
Commodity contract commitments
Commodity contract (in MT/Lbs)			343
Commodity Contract [Member] | Future [Member] | Designated As Hedging Instrument [Member] | Cost Of Sales [Member]
Gains or losses on derivative instruments, statement of income
Amount of gain (loss) recognized in income on derivatives	(2,632,000)	(654,000)	(1,015,000)	7,392,000
Commodity Contract [Member] | Future [Member] | Designated As Hedging Instrument [Member] | Other Current Assets [Member]
Fair values of derivative instruments, balance sheet
Commodity futures, asset derivatives (in dollars)	274,000		274,000		658,000
Commodity futures, liability derivatives (in dollars)	(1,800,000)		(1,800,000)		1,886,000
Commodity Contract [Member] | Future [Member] | Nondesignated [Member] | Cost Of Sales [Member]
Gains or losses on derivative instruments, statement of income
Amount of gain recognized in income on derivatives	(2,030,000)	6,621,000	5,926,000	6,629,000
Commodity Contract [Member] | Future [Member] | Nondesignated [Member] | Other Current Assets [Member]
Fair values of derivative instruments, balance sheet
Commodity futures, asset derivatives (in dollars)	708,000		708,000		352,000
Commodity futures, liability derivatives (in dollars)	(1,781,000)		(1,781,000)		2,601,000
Interest Rate Swap [Member]
Commodity contract commitments
Number of derivative instruments	0	0	0	0
Foreign Exchange Forward [Member]
Commodity contract commitments
Number of derivative instruments	0	0	0	0
Hedged Items Firm Commitment [Member] | Designated As Hedging Instrument [Member] | Cost Of Sales [Member]
Gains or losses on derivative instruments, statement of income
Amount of gain (loss) recognized in income on related hedged items	(653,000)	1,297,000	331,000	2,613,000
Hedged Items Inventory [Member] | Designated As Hedging Instrument [Member] | Cost Of Sales [Member]
Gains or losses on derivative instruments, statement of income
Amount of gain (loss) recognized in income on related hedged items	$ 2,846,000	$ (2,014,000)	$ 358,000	$ (8,822,000)