Supplemental equity information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 24, 2012	Jun. 30, 2013	Jun. 24, 2012
Accumulated Other Comprehensive Income [Line Items]
Balance at	$ (709,334)	$ (580,619)	$ (701,141)	$ (595,839)
Other comprehensive income before reclassifications	(407)	(11,155)	(18,296)	(3,021)
Amounts reclassified from accumulated other comprehensive income	9,970	7,206	19,666	14,292
Other comprehensive income	9,563	(3,949)	1,370	11,271
Balance at	(699,771)	(584,568)	(699,771)	(584,568)
Retirement Plans [Member]
Accumulated Other Comprehensive Income [Line Items]
Balance at	(1,094,870)	(991,640)	(1,119,263)	(995,853)
Other comprehensive income before reclassifications	(120)	1,142	14,577	(1,731)
Amounts reclassified from accumulated other comprehensive income	9,970	7,206	19,666	14,292
Other comprehensive income	9,850	8,348	34,243	12,561
Balance at	(1,085,020)	(983,292)	(1,085,020)	(983,292)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income [Line Items]
Balance at	385,536	411,021	418,122	400,014
Other comprehensive income before reclassifications	(287)	(12,297)	(32,873)	(1,290)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income	(287)	(12,297)	(32,873)	(1,290)
Balance at	$ 385,249	$ 398,724	$ 385,249	$ 398,724