Supplemental equity information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 28, 2014	Sep. 29, 2013	Sep. 28, 2014	Sep. 29, 2013
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	$ (458,542)	$ (699,771)	$ (494,055)	$ (701,141)
Other comprehensive income (loss) before reclassifications	(11,629)	16,455	9,894	(1,841)
Amounts reclassified from accumulated other comprehensive income (loss)	6,817	9,834	20,807	29,500
Other comprehensive income (loss)	(4,812)	26,289	30,701	27,659
Ending Balance	(463,354)	(673,482)	(463,354)	(673,482)
Retirement Plans [Member]
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(903,180)	(1,085,020)	(921,232)	(1,119,263)
Other comprehensive income (loss) before reclassifications	16,783	(14,016)	20,845	561
Amounts reclassified from accumulated other comprehensive income (loss)	6,817	9,834	20,807	29,500
Other comprehensive income (loss)	23,600	(4,182)	41,652	30,061
Ending Balance	(879,580)	(1,089,202)	(879,580)	(1,089,202)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	444,638	385,249	427,177	418,122
Other comprehensive income (loss) before reclassifications	(28,412)	30,471	(10,951)	(2,402)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	0
Other comprehensive income (loss)	(28,412)	30,471	(10,951)	(2,402)
Ending Balance	$ 416,226	$ 415,720	$ 416,226	$ 415,720