Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 30, 2014	Mar. 31, 2013	Dec. 29, 2013
Fair Value of Financial Instruments (Thousands of Dollars) [Abstract]
Fair Value of Available for Sale Investments, Fair Value Option	$ 37,201	$ 23,907	$ 28,048
Net Gain (Loss) on Available-for-Sale Investments, Fair Value Option	1,177	280
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	40,984	23,915	28,048
Derivatives, assets	1,311	12,854	4,627
Total assets, fair value hierarchy	42,295	36,769	32,675
Derivatives, liabilities	33,053	3,231	12,330
Reconciliation of fair value for Level 3 financial instruments
Balance at beginning of year	5,484	7,618
Gain (loss) from change in fair value	179	(1,371)
Balance at end of first quarter	5,663	6,247
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	3,783	8	0
Derivatives, assets	0	0	0
Total assets, fair value hierarchy	3,783	8	0
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	31,538	18,650	22,564
Derivatives, assets	1,311	11,864	4,627
Total assets, fair value hierarchy	32,849	30,514	27,191
Derivatives, liabilities	33,053	3,231	12,330
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	5,663	5,257	5,484
Derivatives, assets	0	990	0
Total assets, fair value hierarchy	5,663	6,247	5,484
Derivatives, liabilities	$ 0	$ 0	$ 0