Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 25, 2011	Sep. 30, 2012	Sep. 25, 2011	Dec. 25, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	$ 23,415	$ 20,119	$ 23,415	$ 20,119	$ 19,669
Derivatives, assets	22,088	35,346	22,088	35,346	29,500
Total assets, fair value hierarchy	45,503	55,465	45,503	55,465	49,169
Derivatives, liabilities	2,312	7,262	2,312	7,262	1,908
Fair Value of Available for Sale Investments, Fair Value Option	23,403	20,095	23,403	20,095	19,657
Gain (Loss) on Available for Sale Investments, Fair Value Option	1,082	(24)	1,847	499
Reconciliation of fair value for Level 3 financial instruments
Balance at beginning of year			3,724	9,155
Purchases			5,000	0
Loss from change in fair value			(1,335)	(6,275)
Balance at end of period	7,389	2,880	7,389	2,880
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	12	24	12	24	12
Derivatives, assets	0	0	0	0	0
Total assets, fair value hierarchy	12	24	12	24	12
Derivatives, liabilities	0	0	0	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	18,403	20,095	18,403	20,095	19,657
Derivatives, assets	19,699	32,466	19,699	32,466	25,776
Total assets, fair value hierarchy	38,102	52,561	38,102	52,561	45,433
Derivatives, liabilities	2,312	7,262	2,312	7,262	1,908
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	5,000	0	5,000	0	0
Derivatives, assets	2,389	2,880	2,389	2,880	3,724
Total assets, fair value hierarchy	7,389	2,880	7,389	2,880	3,724
Derivatives, liabilities	$ 0	$ 0	$ 0	$ 0	$ 0