Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Apr. 01, 2012	Dec. 30, 2012
Fair Value of Financial Instruments (Thousands of Dollars) [Abstract]
Fair Value of Available for Sale Investments, Fair Value Option	$ 23,907	$ 20,190	$ 24,091
Net Gain on Available-for-Sale Investments, Fair Value Option	280	1,096
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	23,915	20,202	24,099
Derivatives, assets	12,854	22,345	4,254
Total assets, fair value hierarchy	36,769	42,547	28,353
Derivatives, liabilities	3,231	6,054	3,461
Reconciliation of fair value for Level 3 financial instruments
Balance at beginning of year	7,618	3,724
Gain (loss) from change in fair value	(1,371)	795
Balance at end of first quarter	6,247	4,519
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
Derivatives, assets	0	0	0
Total assets, fair value hierarchy	8	12	8
Derivatives, liabilities	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	18,650	20,190	18,986
Derivatives, assets	11,864	17,826	1,741
Total assets, fair value hierarchy	30,514	38,016	20,727
Derivatives, liabilities	3,231	6,054	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	5,257	0	5,105
Derivatives, assets	990	4,519	2,513
Total assets, fair value hierarchy	6,247	4,519	7,618
Derivatives, liabilities	$ 0	$ 0	$ 0