Derivatives and Fair Value of Financial Instruments (Details) (USD $)	3 Months Ended
	Apr. 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	21,752,000	4,314,000
Money market funds
Assets:
Available-for-sale securities	236,974,000	142,432,000
Corporate bonds
Assets:
Available-for-sale securities	11,757,000	11,015,000
U.S. Government agency securities
Assets:
Available-for-sale securities	9,354,000	9,666,000
Asset backed debt securities
Assets:
Available-for-sale securities	2,554,000	2,291,000
U.S. Treasury securities
Assets:
Available-for-sale securities	1,996,000	522,000
Collateralized mortgage obligations
Assets:
Available-for-sale securities	816,000	1,170,000
High yield debt securities
Assets:
Trading securities	175,390,000	181,483,000
Equity mutual fund
Assets:
Trading securities	86,268,000	82,542,000
Domestic equity ETF
Assets:
Trading securities	61,806,000	32,651,000
Money market funds held in trading accounts
Assets:
Trading securities	6,362,000	21,401,000
Emerging markets trading debt mutual fund
Assets:
Trading securities	2,550,000	2,614,000
Recurring basis | Fair Value
Assets:
Total Assets	652,559,000	546,012,000
Liabilities:
Liabilities	19,402,000	9,901,000
Recurring basis | Fair Value | Commodities
Assets:
Derivatives	4,147,000	6,136,000
Margin account	21,752,000	4,314,000
Liabilities:
Derivatives	9,722,000	1,779,000
Recurring basis | Fair Value | Interest rate swaps
Liabilities:
Derivatives	9,256,000	7,715,000
Recurring basis | Fair Value | Foreign currencies
Assets:
Derivatives	1,039,000	1,675,000
Liabilities:
Derivatives	424,000	407,000
Recurring basis | Fair Value | Other current assets | Commodities
Assets:
Derivative assets and liabilities, net basis	16,612,000	9,267,000
Recurring basis | Fair Value | Other current liabilities | Commodities
Liabilities:
Derivatives	435,000	596,000
Recurring basis | Fair Value | Money market funds
Assets:
Available-for-sale securities	236,974,000
Recurring basis | Fair Value | Money market funds | Short-term investments.
Assets:
Available-for-sale securities		142,432,000
Recurring basis | Fair Value | Corporate bonds
Assets:
Available-for-sale securities	11,757,000
Recurring basis | Fair Value | Corporate bonds | Short-term investments.
Assets:
Available-for-sale securities		11,015,000
Recurring basis | Fair Value | U.S. Government agency securities
Assets:
Available-for-sale securities	9,354,000
Recurring basis | Fair Value | U.S. Government agency securities | Short-term investments.
Assets:
Available-for-sale securities		9,666,000
Recurring basis | Fair Value | Asset backed debt securities
Assets:
Available-for-sale securities	2,554,000
Recurring basis | Fair Value | Asset backed debt securities | Short-term investments.
Assets:
Available-for-sale securities		2,291,000
Recurring basis | Fair Value | U.S. Treasury securities | Short-term investments.
Assets:
Available-for-sale securities	1,996,000	522,000
Recurring basis | Fair Value | Collateralized mortgage obligations
Assets:
Available-for-sale securities	816,000
Recurring basis | Fair Value | Collateralized mortgage obligations | Short-term investments.
Assets:
Available-for-sale securities		1,170,000
Recurring basis | Fair Value | High yield debt securities | Short-term investments.
Assets:
Trading securities	175,390,000	181,483,000
Recurring basis | Fair Value | Equity mutual fund | Short-term investments.
Assets:
Trading securities	86,268,000	82,542,000
Recurring basis | Fair Value | Domestic equity ETF | Short-term investments.
Assets:
Trading securities	61,806,000	32,651,000
Recurring basis | Fair Value | Money market funds held in trading accounts | Short-term investments.
Assets:
Trading securities	6,362,000	21,401,000
Recurring basis | Fair Value | Emerging markets trading debt mutual fund | Short-term investments.
Assets:
Trading securities	2,550,000	2,614,000
Recurring basis | Fair Value | Other trading investments | Short-term investments.
Assets:
Trading securities	1,792,000	2,779,000
Recurring basis | Fair Value | Domestic equity securities | Other current assets
Assets:
Trading securities	35,600,000	33,857,000
Recurring basis | Fair Value | Foreign equity securities | Other current assets
Assets:
Trading securities	6,780,000	6,532,000
Recurring basis | Fair Value | Fixed income mutual funds | Other current assets
Assets:
Trading securities	4,415,000	4,570,000
Recurring basis | Fair Value | Other | Other current assets
Assets:
Trading securities	2,959,000	2,676,000
Recurring basis | Level 1
Assets:
Total Assets	447,413,000	335,140,000
Liabilities:
Liabilities	9,722,000	1,779,000
Recurring basis | Level 1 | Commodities
Assets:
Derivatives	4,147,000	6,136,000
Liabilities:
Derivatives	9,722,000	1,779,000
Recurring basis | Level 1 | Money market funds
Assets:
Available-for-sale securities	236,974,000
Recurring basis | Level 1 | Money market funds | Short-term investments.
Assets:
Available-for-sale securities		142,432,000
Recurring basis | Level 1 | Equity mutual fund | Short-term investments.
Assets:
Trading securities	86,268,000	82,542,000
Recurring basis | Level 1 | Domestic equity ETF | Short-term investments.
Assets:
Trading securities	61,806,000	32,651,000
Recurring basis | Level 1 | Money market funds held in trading accounts | Short-term investments.
Assets:
Trading securities	6,362,000	21,401,000
Recurring basis | Level 1 | Emerging markets trading debt mutual fund | Short-term investments.
Assets:
Trading securities	2,550,000	2,614,000
Recurring basis | Level 1 | Domestic equity securities | Other current assets
Assets:
Trading securities	35,600,000	33,857,000
Recurring basis | Level 1 | Foreign equity securities | Other current assets
Assets:
Trading securities	6,780,000	6,532,000
Recurring basis | Level 1 | Fixed income mutual funds | Other current assets
Assets:
Trading securities	4,415,000	4,570,000
Recurring basis | Level 1 | Other | Other current assets
Assets:
Trading securities	2,511,000	2,405,000
Recurring basis | Level 2
Assets:
Total Assets	205,146,000	210,872,000
Liabilities:
Liabilities	9,680,000	8,122,000
Recurring basis | Level 2 | Interest rate swaps
Liabilities:
Derivatives	9,256,000	7,715,000
Recurring basis | Level 2 | Foreign currencies
Assets:
Derivatives	1,039,000	1,675,000
Liabilities:
Derivatives	424,000	407,000
Recurring basis | Level 2 | Corporate bonds
Assets:
Available-for-sale securities	11,757,000
Recurring basis | Level 2 | Corporate bonds | Short-term investments.
Assets:
Available-for-sale securities		11,015,000
Recurring basis | Level 2 | U.S. Government agency securities
Assets:
Available-for-sale securities	9,354,000
Recurring basis | Level 2 | U.S. Government agency securities | Short-term investments.
Assets:
Available-for-sale securities		9,666,000
Recurring basis | Level 2 | Asset backed debt securities
Assets:
Available-for-sale securities	2,554,000
Recurring basis | Level 2 | Asset backed debt securities | Short-term investments.
Assets:
Available-for-sale securities		2,291,000
Recurring basis | Level 2 | U.S. Treasury securities | Short-term investments.
Assets:
Available-for-sale securities	1,996,000	522,000
Recurring basis | Level 2 | Collateralized mortgage obligations
Assets:
Available-for-sale securities	816,000
Recurring basis | Level 2 | Collateralized mortgage obligations | Short-term investments.
Assets:
Available-for-sale securities		1,170,000
Recurring basis | Level 2 | High yield debt securities | Short-term investments.
Assets:
Trading securities	175,390,000	181,483,000
Recurring basis | Level 2 | Other trading investments | Short-term investments.
Assets:
Trading securities	1,792,000	2,779,000
Recurring basis | Level 2 | Other | Other current assets
Assets:
Trading securities	$ 448,000	$ 271,000