Derivatives and Fair Value of Financial Instruments (Details) - USD ($)	6 Months Ended
	Jul. 04, 2015	Dec. 31, 2014
Derivatives and Fair Value of Financial Instruments
Transfers that occurred into or out of level 1	$ 0
Transfers that occurred into or out of level 2	0
Transfers that occurred into or out of level 3	0
Commodities
Assets:
Margin account	10,168,000	$ 4,314,000
Money market funds
Assets:
Available-for-sale securities	266,106,000	142,432,000
Corporate bonds
Assets:
Available-for-sale securities	12,538,000	11,015,000
U.S. Government agency securities
Assets:
Available-for-sale securities	9,480,000	9,666,000
Other available-for-sale investments
Assets:
Available-for-sale securities	3,706,000	3,983,000
High yield trading debt securities
Assets:
Trading securities	159,798,000	181,483,000
Equity mutual fund
Assets:
Trading securities	84,557,000	82,542,000
Domestic equity ETF
Assets:
Trading securities	61,914,000	32,651,000
Money market funds held in trading accounts
Assets:
Trading securities	23,618,000	21,401,000
Recurring basis | Fair Value
Assets:
Total Assets	700,737,000	546,012,000
Liabilities:
Liabilities	18,484,000	9,901,000
Recurring basis | Fair Value | Commodities
Assets:
Derivatives	20,737,000	6,136,000
Margin account	10,168,000	4,314,000
Liabilities:
Derivatives	11,530,000	1,779,000
Recurring basis | Fair Value | Interest rate swaps
Assets:
Derivatives	1,368,000
Liabilities:
Derivatives	5,348,000	7,715,000
Recurring basis | Fair Value | Foreign currencies
Assets:
Derivatives	2,285,000	1,675,000
Liabilities:
Derivatives	1,606,000	407,000
Recurring basis | Fair Value | Other current assets | Commodities
Assets:
Derivative assets and liabilities, net basis	19,852,000	9,267,000
Recurring basis | Fair Value | Other current liabilities | Commodities
Liabilities:
Derivatives	477,000	596,000
Recurring basis | Fair Value | Money market funds | Short-term investments.
Assets:
Available-for-sale securities	266,106,000	142,432,000
Recurring basis | Fair Value | Corporate bonds | Short-term investments.
Assets:
Available-for-sale securities	12,538,000	11,015,000
Recurring basis | Fair Value | U.S. Government agency securities | Short-term investments.
Assets:
Available-for-sale securities	9,480,000	9,666,000
Recurring basis | Fair Value | Other available-for-sale investments | Short-term investments.
Assets:
Available-for-sale securities	3,706,000	3,983,000
Recurring basis | Fair Value | High yield trading debt securities | Short-term investments.
Assets:
Trading securities	159,798,000	181,483,000
Recurring basis | Fair Value | Equity mutual fund | Short-term investments.
Assets:
Trading securities	84,557,000	82,542,000
Recurring basis | Fair Value | Domestic equity ETF | Short-term investments.
Assets:
Trading securities	61,914,000	32,651,000
Recurring basis | Fair Value | Money market funds held in trading accounts | Short-term investments.
Assets:
Trading securities	23,618,000	21,401,000
Recurring basis | Fair Value | Other trading investments | Short-term investments.
Assets:
Trading securities	4,820,000	5,393,000
Recurring basis | Fair Value | Domestic equity securities | Other current assets
Assets:
Trading securities	36,294,000	33,857,000
Recurring basis | Fair Value | Foreign equity securities | Other current assets
Assets:
Trading securities	7,010,000	6,532,000
Recurring basis | Fair Value | Fixed income mutual funds | Other current assets
Assets:
Trading securities	3,587,000	4,570,000
Recurring basis | Fair Value | Other | Other current assets
Assets:
Trading securities	2,919,000	2,676,000
Recurring basis | Level 1
Assets:
Total Assets	508,796,000	335,140,000
Liabilities:
Liabilities	11,530,000	1,779,000
Recurring basis | Level 1 | Commodities
Assets:
Derivatives	20,737,000	6,136,000
Liabilities:
Derivatives	11,530,000	1,779,000
Recurring basis | Level 1 | Money market funds | Short-term investments.
Assets:
Available-for-sale securities	266,106,000	142,432,000
Recurring basis | Level 1 | Equity mutual fund | Short-term investments.
Assets:
Trading securities	84,557,000	82,542,000
Recurring basis | Level 1 | Domestic equity ETF | Short-term investments.
Assets:
Trading securities	61,914,000	32,651,000
Recurring basis | Level 1 | Money market funds held in trading accounts | Short-term investments.
Assets:
Trading securities	23,618,000	21,401,000
Recurring basis | Level 1 | Other trading investments | Short-term investments.
Assets:
Trading securities	2,453,000	2,614,000
Recurring basis | Level 1 | Domestic equity securities | Other current assets
Assets:
Trading securities	36,294,000	33,857,000
Recurring basis | Level 1 | Foreign equity securities | Other current assets
Assets:
Trading securities	7,010,000	6,532,000
Recurring basis | Level 1 | Fixed income mutual funds | Other current assets
Assets:
Trading securities	3,587,000	4,570,000
Recurring basis | Level 1 | Other | Other current assets
Assets:
Trading securities	2,520,000	2,405,000
Recurring basis | Level 2
Assets:
Total Assets	191,941,000	210,872,000
Liabilities:
Liabilities	6,954,000	8,122,000
Recurring basis | Level 2 | Interest rate swaps
Assets:
Derivatives	1,368,000
Liabilities:
Derivatives	5,348,000	7,715,000
Recurring basis | Level 2 | Foreign currencies
Assets:
Derivatives	2,285,000	1,675,000
Liabilities:
Derivatives	1,606,000	407,000
Recurring basis | Level 2 | Corporate bonds | Short-term investments.
Assets:
Available-for-sale securities	12,538,000	11,015,000
Recurring basis | Level 2 | U.S. Government agency securities | Short-term investments.
Assets:
Available-for-sale securities	9,480,000	9,666,000
Recurring basis | Level 2 | Other available-for-sale investments | Short-term investments.
Assets:
Available-for-sale securities	3,706,000	3,983,000
Recurring basis | Level 2 | High yield trading debt securities | Short-term investments.
Assets:
Trading securities	159,798,000	181,483,000
Recurring basis | Level 2 | Other trading investments | Short-term investments.
Assets:
Trading securities	2,367,000	2,779,000
Recurring basis | Level 2 | Other | Other current assets
Assets:
Trading securities	$ 399,000	$ 271,000