Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jul. 01, 2012	Jun. 30, 2013	Jul. 01, 2012	Dec. 30, 2012
Fair Value of Financial Instruments (Thousands of Dollars) [Abstract]
Fair Value of Available for Sale Investments, Fair Value Option	$ 23,633	$ 19,589	$ 23,633	$ 19,589	$ 24,091
Net Gain (Loss) on Available-for-Sale Investments, Fair Value Option	(271)	(331)	9	765
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	23,641	19,871	23,641	19,871	24,099
Derivatives, assets	16,890	33,045	16,890	33,045	4,254
Total assets, fair value hierarchy	40,531	52,916	40,531	52,916	28,353
Derivatives, liabilities	1,235	765	1,235	765	3,461
Reconciliation of fair value for Level 3 financial instruments
Balance at beginning of year			7,618	3,724
Loss from change in fair value			(1,239)	(398)
Balance at end of second quarter	6,379	3,326	6,379	3,326
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	8	12	8	12	8
Derivatives, assets	0	0	0	0	0
Total assets, fair value hierarchy	8	12	8	12	8
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	18,244	19,859	18,244	19,859	18,986
Derivatives, assets	15,900	29,719	15,900	29,719	1,741
Total assets, fair value hierarchy	34,144	49,578	34,144	49,578	20,727
Derivatives, liabilities	1,235	765	1,235	765	3,461
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	5,389	0	5,389	0	5,105
Derivatives, assets	990	3,326	990	3,326	2,513
Total assets, fair value hierarchy	6,379	3,326	6,379	3,326	7,618
Derivatives, liabilities	$ 0	$ 0	$ 0	$ 0	$ 0