Financial Instruments (Narrative) (Details) (USD $)			3 Months Ended		6 Months Ended
	Jun. 27, 2014 derivatives	Dec. 31, 2013 derivatives	Jun. 27, 2014 Not Designated as Hedging Instrument [Member]	Jun. 28, 2013 Not Designated as Hedging Instrument [Member]	Jun. 27, 2014 Not Designated as Hedging Instrument [Member]	Jun. 28, 2013 Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative contracts held that require collateral securities	$ 0	$ 0
Number of derivative require collateral security	0	0
Gain (loss) on derivative instruments not designated as cash flow hedges			(3,900,000)	(10,300,000)	(10,700,000)	(20,400,000)
Forward pricing agreements	31,300,000	10,100,000
Fair value forward pricing agreements	31,500,000	10,600,000
Unrealized gain (loss) related to forward pricing agreements	$ (200,000)	$ 500,000