Shareholders' Equity - Changes in AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 28, 2018	Sep. 29, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Accumulated other comprehensive income (loss)	$ (146,074)	$ (122,580)	$ (127,789)	$ (142,228)
Other comprehensive income (loss) before reclassifications	4,161	574	(2,205)	17,921
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,524	1,453	5,058	3,754
Reclassified to Retained Earnings from AOCI			(15,453)
Ending Accumulated other comprehensive income (loss)	(140,389)	(120,553)	(140,389)	(120,553)
Pension and Postretirement Medical
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Accumulated other comprehensive income (loss)	(90,349)	(74,125)	(78,430)	(76,426)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,524	1,453	5,058	3,754
Reclassified to Retained Earnings from AOCI			(15,453)
Ending Accumulated other comprehensive income (loss)	(88,825)	(72,672)	(88,825)	(72,672)
Cumulative Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Accumulated other comprehensive income (loss)	(55,725)	(48,455)	(49,359)	(65,802)
Other comprehensive income (loss) before reclassifications	4,161	574	(2,205)	17,921
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0	0
Reclassified to Retained Earnings from AOCI			0
Ending Accumulated other comprehensive income (loss)	$ (51,564)	$ (47,881)	$ (51,564)	$ (47,881)