Supplemental equity information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2014	Jun. 30, 2013	Jun. 29, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	$ (467,196)	$ (709,334)	$ (494,055)	$ (701,141)
Other comprehensive income (loss) before reclassifications	1,766	(407)	21,523	(18,296)
Amounts reclassified from accumulated other comprehensive income (loss)	6,888	9,970	13,990	19,666
Other comprehensive income (loss)	8,654	9,563	35,513	1,370
Ending Balance	(458,542)	(699,771)	(458,542)	(699,771)
Retirement Plans [Member]
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(899,026)	(1,094,870)	(921,232)	(1,119,263)
Other comprehensive income (loss) before reclassifications	(11,042)	(120)	4,062	14,577
Amounts reclassified from accumulated other comprehensive income (loss)	6,888	9,970	13,990	19,666
Other comprehensive income (loss)	(4,154)	9,850	18,052	34,243
Ending Balance	(903,180)	(1,085,020)	(903,180)	(1,085,020)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	431,830	385,536	427,177	418,122
Other comprehensive income (loss) before reclassifications	12,808	(287)	17,461	(32,873)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	0
Other comprehensive income (loss)	12,808	(287)	17,461	(32,873)
Ending Balance	$ 444,638	$ 385,249	$ 444,638	$ 385,249