Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2015	Sep. 28, 2014	Sep. 27, 2015	Sep. 28, 2014	Dec. 28, 2014
Fair Value of Financial Instruments (Thousands of Dollars) [Abstract]
Fair Value of Available for Sale Investments, Fair Value Option	$ 22,834	$ 24,292	$ 22,834	$ 24,292	$ 23,560
Net Gain (Loss) on Available-for-Sale Investments, Fair Value Option	(176)	247	(246)	2,487
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	26,863	31,097	26,863	31,097	28,042
Derivatives, assets	119,123	41,475	119,123	41,475	69,148
Total assets, fair value hierarchy	145,986	72,572	145,986	72,572	97,190
Derivatives, liabilities	605	3,426	605	3,426	2,591
Option Agreement	24,780	25,590	24,780	25,590	25,340
Total Liabilities	25,385	29,016	25,385	29,016	27,931
Reconciliation of fair value for Level 3 financial instruments
Balance at beginning of year			(19,553)	5,484
Purchases			5,000	0
Gain from change in fair value			943	176
Issuance of option agreement			0	(25,590)
Balance at end of period	(13,610)	(19,930)	(13,610)	(19,930)
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	4,029	6,805	4,029	6,805	4,482
Derivatives, assets	0	0	0	0	0
Total assets, fair value hierarchy	4,029	6,805	4,029	6,805	4,482
Derivatives, liabilities	0	0	0	0	0
Option Agreement	0	0	0	0	0
Total 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	11,664	18,632	11,664	18,632	17,773
Derivatives, assets	119,123	41,475	119,123	41,475	69,148
Total assets, fair value hierarchy	130,787	60,107	130,787	60,107	86,921
Derivatives, liabilities	605	3,426	605	3,426	2,591
Option Agreement	0	0	0	0	0
Total Liabilities	605	3,426	605	3,426	2,591
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, assets	11,170	5,660	11,170	5,660	5,787
Derivatives, assets	0	0	0	0	0
Total assets, fair value hierarchy	11,170	5,660	11,170	5,660	5,787
Derivatives, liabilities	0	0	0	0	0
Option Agreement	24,780	25,590	24,780	25,590	25,340
Total Liabilities	$ 24,780	$ 25,590	$ 24,780	$ 25,590	$ 25,340