Long-term debt (Details) (USD $) In Thousands, unless otherwise specified	Jun. 24, 2012	Dec. 25, 2011
Summary Long-term debt
Long-term Debt	$ 1,662,782	$ 1,760,363
Unsecured notes bearing fixed rate interest at 6.375% repaid April 2012 [Member]
Summary Long-term debt
Long-term Debt		306,534
Borrowings under revolving credit agreements expiring September 2014 [Member]
Summary Long-term debt
Long-term Debt	440,000	235,000
Unsecured notes bearing fixed rate interest at 8.75% due November 2014 [Member]
Summary Long-term debt
Long-term Debt	247,977	247,609
Unsecured notes bearing fixed rate interest at 10% due June 2015 [Member]
Summary Long-term debt
Long-term Debt	60,360	59,522
Unsecured notes bearing fixed rate interest at 6.375% due September 2015 [Member]
Summary Long-term debt
Long-term Debt	248,236	247,995
Unsecured notes bearing fixed rate interest at 10% due April 2016 [Member]
Summary Long-term debt
Long-term Debt	171,912	169,775
Unsecured notes bearing fixed rate interest at 9.375% due November 2017 [Member]
Summary Long-term debt
Long-term Debt	247,349	247,168
Unsecured notes bearing fixed rate interest at 7.125% due September 2018 [Member]
Summary Long-term debt
Long-term Debt	$ 246,948	$ 246,760