Long-term debt (Details Textual) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 30, 2012	Jul. 29, 2013 Unsecured Fixed Rate Notes 5.125 Percent Due 2020 [Member] Subsequent Event [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate, stated percentage			5.125%
Long-term Debt (Textual) [Abstract]
Reduction in long-term debt reflecting repayments of borrowings, net of discount amortization	$ 74,600,000
Revolving credit agreements, repayments	79,000,000
Line of credit facility, unused borrowing capacity	980,300,000
Long-term Debt	$ 1,357,501,000	$ 1,432,100,000
Debt Instrument Offering Price Percentage			98.566%
Debt Instrument Yield To Maturity			5.375%