Changes in shareholders' equity Change in accumulated other comprehensive income , net of tax (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 29, 2015	Mar. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss)	$ (260,895)	$ (110,855)
Other comprehensive income (loss) before reclassifications	(82,098)	4,005
Amounts reclassified from accumulated other comprehensive (loss) income	897	740
Net current-period other comprehensive income (loss)	(81,201)	4,745
Ending balance, accumulated other comprehensive income (loss)	(342,096)	(106,110)
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss)	0	0
Other comprehensive income (loss) before reclassifications	243	113
Amounts reclassified from accumulated other comprehensive (loss) income	(199)	(43)
Net current-period other comprehensive income (loss)	44	70
Ending balance, accumulated other comprehensive income (loss)	44	70
Pension and Other Postretirement Benefits Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss)	(141,744)	(97,037)
Other comprehensive income (loss) before reclassifications	810	(159)
Amounts reclassified from accumulated other comprehensive (loss) income	1,096	783
Net current-period other comprehensive income (loss)	1,906	624
Ending balance, accumulated other comprehensive income (loss)	(139,838)	(96,413)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss)	(119,151)	(13,818)
Other comprehensive income (loss) before reclassifications	(83,151)	4,051
Amounts reclassified from accumulated other comprehensive (loss) income	0	0
Net current-period other comprehensive income (loss)	(83,151)	4,051
Ending balance, accumulated other comprehensive income (loss)	$ (202,302)	$ (9,767)

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14A

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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