Financial Instruments Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Jan. 02, 2013	Dec. 31, 2012	Jan. 02, 2012	Dec. 31, 2011	Jan. 02, 2011
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash and Cash Equivalents	$ 327,420	$ 21,862	$ 21,862	$ 375,736	$ 375,736	$ 32,794
Short-term Non-bank Loans and Notes Payable	0		25,073
Borrowings Under Securitization Facility	0		37,846
Long-term Debt	3,118,920		3,127,726
Quoted Prices in Active Markets for Identical Liabilities (Level 1)
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Gas Cash Flow hedges	0		0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Gas Cash Flow hedges	65,449		128,945
Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Gas Cash Flow hedges	0		0
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash and Investments	20,379
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash and Cash Equivalents	327,420		21,862
Restricted Cash and Cash Equivalents	0		68,673
Short-term Non-bank Loans and Notes Payable	0		25,073
Borrowings Under Securitization Facility	0		37,846
Long-term Debt	3,118,920		3,127,726
Fair Value
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash and Cash Equivalents	327,420		21,862
Restricted Cash and Cash Equivalents	0		68,673
Short-term Non-bank Loans and Notes Payable	0		25,073
Borrowings Under Securitization Facility	0		37,846
Long-term Debt	$ 3,299,875		$ 3,376,767