Debt (Senior Notes) (Details) (USD $)	3 Months Ended		0 Months Ended		3 Months Ended	12 Months Ended	0 Months Ended	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012	Jan. 31, 2013 3.85% Senior Notes Due February 1,2023 [Member]	Jan. 17, 2006 6.125% Notes, Payable January 15, 2016 [Member]	Mar. 31, 2012 6.125% Notes, Payable January 15, 2016 [Member]	Dec. 31, 2009 6.125% Notes, Payable January 15, 2016 [Member]	Apr. 16, 2012 7.20% Senior Notes, Payable April 15, 2012 [Member]	Mar. 30, 2013 7.20% Senior Notes, Payable April 15, 2012 [Member]	Mar. 31, 2012 7.20% Senior Notes, Payable April 15, 2012 [Member]	Dec. 31, 2002 7.20% Senior Notes, Payable April 15, 2012 [Member]
Debt Instrument [Line Items]
Aggregate principal amount of debts			$ 600,000,000	$ 900,000,000						$ 400,000,000
Interest rate percentage			3.85%	6.125%				7.20%	7.20%
Payment of financing costs			5,150,000
Notes payable, maturity date				Jan. 15, 2016				Apr. 15, 2012
Increase in interest rate from rating agency downgrade				0.25%
Maximum increase in interest rate per agency from rating agency downgrade				1.00%
Aggregate amount of increase in interest rate from rating agency downgrade						0.75%
Aggregate amount of decrease in interest rate from rating agency downgrade					0.50%
Increase in interest expense per quarter for .25% increase in notes per $100,000 of outstanding notes	19,156,000	22,498,000		63,000
Incremental increase in outstanding notes				100,000
Remaining outstanding senior notes repaid									63,730,000
Repurchase price as percentage of principal amount of senior notes									102.72%
Company repaid principal amount							336,270,000
Debt instruments interest accrued							$ 12,106,000