Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2014	Jun. 30, 2013	Jun. 29, 2014	Jun. 30, 2013	Dec. 29, 2013
Fair Value of Financial Instruments (Thousands of Dollars) [Abstract]
Fair Value of Available for Sale Investments, Fair Value Option	$ 33,528	$ 23,633	$ 33,528	$ 23,633	$ 28,048
Net Gain (Loss) on Available-for-Sale Investments, Fair Value Option	1,063	(271)	2,240	9
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	40,712	23,641	40,712	23,641	28,048
Derivatives, assets	533	16,890	533	16,890	4,627
Total assets, fair value hierarchy	41,245	40,531	41,245	40,531	32,675
Derivatives, liabilities	16,131	1,235	16,131	1,235	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			133	(1,239)
Balance at end of second quarter	5,617	6,379	5,617	6,379
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	7,183	8	7,183	8	0
Derivatives, assets	0	0	0	0	0
Total assets, fair value hierarchy	7,183	8	7,183	8	0
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	27,912	18,244	27,912	18,244	22,564
Derivatives, assets	533	15,900	533	15,900	4,627
Total assets, fair value hierarchy	28,445	34,144	28,445	34,144	27,191
Derivatives, liabilities	16,131	1,235	16,131	1,235	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	5,617	5,389	5,617	5,389	5,484
Derivatives, assets	0	990	0	990	0
Total assets, fair value hierarchy	5,617	6,379	5,617	6,379	5,484
Derivatives, liabilities	$ 0	$ 0	$ 0	$ 0	$ 0