Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 29, 2013	Sep. 30, 2012	Sep. 29, 2013	Sep. 30, 2012	Dec. 30, 2012
Fair Value of Financial Instruments (Thousands of Dollars) [Abstract]
Fair Value of Available for Sale Investments, Fair Value Option	$ 23,452	$ 23,403	$ 23,452	$ 23,403	$ 24,091
Net Gain (Loss) on Available-for-Sale Investments, Fair Value Option	(176)	1,082	(166)	1,847
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	23,460	23,415	23,460	23,415	24,099
Derivatives, assets	3,311	22,088	3,311	22,088	4,254
Total assets, fair value hierarchy	26,771	45,503	26,771	45,503	28,353
Derivatives, liabilities	8,324	2,312	8,324	2,312	3,461
Reconciliation of fair value for Level 3 financial instruments
Balance at beginning of year			7,618	3,724
Purchases			0	5,000
Loss from change in fair value			(1,226)	(1,335)
Balance at end of third quarter	6,392	7,389	6,392	7,389
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	18,050	18,403	18,050	18,403	18,986
Derivatives, assets	2,321	19,699	2,321	19,699	1,741
Total assets, fair value hierarchy	20,371	38,102	20,371	38,102	20,727
Derivatives, liabilities	8,324	2,312	8,324	2,312	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	5,402	5,000	5,402	5,000	5,105
Derivatives, assets	990	2,389	990	2,389	2,513
Total assets, fair value hierarchy	6,392	7,389	6,392	7,389	7,618
Derivatives, liabilities	$ 0	$ 0	$ 0	$ 0	$ 0