Long-term debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 30, 2012
Summary Long-term debt
Long-term Debt	$ 1,449,226		$ 1,432,100
Borrowings under revolving credit agreements expiring September 2014 [Member]
Summary Long-term debt
Long-term Debt	220,000		205,000
Unsecured notes bearing fixed rate interest at 8.75% due November 2014 [Member]
Summary Long-term debt
Long-term Debt	248,578		248,376
Long-term debt, interest rate	8.75%
Unsecured notes bearing fixed rate interest at 10% due June 2015 [Member]
Summary Long-term debt
Long-term Debt	61,743		61,286
Long-term debt, interest rate	10.00%
Unsecured notes bearing fixed rate interest at 6.375% due September 2015 [Member]
Summary Long-term debt
Long-term Debt	248,626		248,497
Long-term debt, interest rate	6.375%
Unsecured notes bearing fixed rate interest at 10% due April 2016 [Member]
Summary Long-term debt
Long-term Debt	175,378		174,241
Long-term debt, interest rate	10.00%
Unsecured notes bearing fixed rate interest at 9.375% due November 2017 [Member]
Summary Long-term debt
Long-term Debt	247,647	[1]	247,547	[1]
Long-term debt, interest rate	9.375%
Unsecured notes bearing fixed rate interest at 7.125% due September 2018 [Member]
Summary Long-term debt
Long-term Debt	$ 247,254		$ 247,153
Long-term debt, interest rate	7.125%
If redeemed during the 12-month period commencing on November 15 , 2013 | Unsecured notes bearing fixed rate interest at 9.375% due November 2017 [Member]
Debt Instrument [Line Items]
Debt Instrument Redemption Price	104.688%

[1] Callable commencing on November 15, 2013 at 104.688% of the principal amount.