Debt (Details) (USD $)	6 Months Ended		1 Months Ended				1 Months Ended	6 Months Ended
	Jul. 01, 2012	Jan. 01, 2012	May 30, 2008 2015 Notes [Member]	Jul. 01, 2012 2015 Notes [Member]	Jul. 01, 2012 2021 Notes [Member]	Jan. 01, 2012 2021 Notes [Member]	Oct. 25, 2011 2021 Notes [Member] Issuance of Debt [Member]	Jul. 01, 2012 Unsecured Revolving Credit Facility [Member]	Jul. 01, 2012 Unsecured Revolving Credit Facility [Member] Eurocurrency Rate [Member]	Jul. 01, 2012 Unsecured Revolving Credit Facility [Member] Base Rate Option Two [Member]
Unsecured revolving credit facility, amount	$ 700,000,000
Unsecured revolving credit facility, expiry date	12/16/2016
Letters of credit issued and outstanding								12,000,000
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 corporate base rate announced from time to time by Bank of America, N.A. or (ii) the Federal Funds rate plus 50 basis points.
Weighted average interest rates under amended senior unsecured revolving credit facility								The Eurocurrency margin as of July 1, 2012 was 130 basis points. The weighted average Eurocurrency interest rate as of July 1, 2012 was 0.24%, resulting in a weighted average effective Eurocurrency rate, including the margin, of 1.54%.
Description of variable rate basis									Eurocurrency	Federal Funds
Basis spread on variable rate									1.30%	0.50%
Weighted average Eurocurrency interest rate									0.24%
Weighted average effective Eurocurrency rate, including the margin									1.54%
Aggregate borrowings under the amended facility	264,000,000	298,000,000
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					$ 3,000,000	$ 3,100,000	$ 3,100,000
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%