Debt (Details) (USD $)	6 Months Ended		1 Months Ended		1 Months Ended				6 Months Ended			6 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 30, 2012	May 30, 2008 2015 Notes [Member]	Jun. 30, 2013 2015 Notes [Member]	Oct. 25, 2011 2021 Notes [Member]	Jun. 30, 2013 2021 Notes [Member]	Dec. 30, 2012 2021 Notes [Member]	Jun. 30, 2013 2021 Notes [Member] Treasury Rate [Member]	Jun. 30, 2013 Financing Lease Obligations [Member]	Dec. 30, 2012 Financing Lease Obligations [Member]	Sep. 30, 2012 Financing Lease Obligations [Member]	Jun. 30, 2013 Unsecured Revolving Credit Facility [Member]	Jun. 30, 2013 Unsecured Revolving Credit Facility [Member] Base Rate Option Three [Member]	Jun. 30, 2013 Unsecured Revolving Credit Facility [Member] Base Rate Option Two [Member]	Jun. 30, 2013 Unsecured Revolving Credit Facility [Member] Eurocurrency Rate [Member]	Oct. 25, 2011 Issuance of Debt [Member] 2021 Notes [Member]
Unsecured revolving credit facility, amount	$ 700,000,000
Unsecured revolving credit facility, expiry date	Dec. 16, 2016
Letters of credit issued and outstanding												12,300,000
Line of Credit Facility, Remaining Borrowing Capacity	371,700,000
Interest rate terms under amended senior unsecured revolving credit facility												The interest rates under the senior unsecured revolving credit facility are based on the Eurocurrency rate at the time of borrowing plus a margin, or the base rate from time to time. The base rate is the higher of (i) the rate of interest in effect for such day as publicly announced from time to time by Bank of America, N.A. as its "prime rate," (ii) the Federal Funds rate plus 50 basis points or (iii) one-month Libor plus 1.00%.
Weighted average interest rates under amended senior unsecured revolving credit facility												The Eurocurrency margin as of June 30, 2013 was 130 basis points. The weighted average Eurocurrency interest rate as of June 30, 2013 was 0.19%, resulting in a weighted average effective Eurocurrency rate, including the margin, of 1.49%.
Description of variable rate basis														Federal Funds	Eurocurrency
Basis spread on variable rate								0.45%					1.00%	0.50%	1.30%
Weighted average Eurocurrency interest rate															0.19%
Weighted average effective Eurocurrency rate, including the margin															1.49%
Aggregate borrowings under the amended facility	316,000,000	258,000,000
Unsecured senior notes, interest rate percent			6.00%		5.00%
Unsecured senior notes, face value			150,000,000	150,000,000	500,000,000	500,000,000
Gross proceeds from the issuance of debt instrument			150,000,000		496,900,000
Senior unsecured notes issuance as percentage of principal amount					99.372%
Debt Instrument, Unamortized Discount					3,100,000	2,700,000	2,800,000
Debt instrument maturity date			May 30, 2015		Nov. 25, 2021
Percentage of redemption of senior notes on or after August 15, 2021																100.00%
Percentage of redemption upon a change of control and a contemporaneous downgrade of the Notes					101.00%
Initial Fair Value of Other Long-term Debt Related to Financing Lease Obligations											29,300,000
Other Long-term Debt									40,800,000	34,600,000
Other Long-term Debt, Current									2,200,000	1,700,000
Other Long-term Debt, Noncurrent									38,600,000	32,900,000
Maximum Additional Financing Lease Obligations									15,000,000
Additional Financing Lease Obligations									$ 11,800,000