Shareholders' Equity and Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2018	Jun. 30, 2017	Jun. 29, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign currency translation adjustments	$ (11,969)	$ 13,777	$ (5,956)	$ 16,374
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			635,656	565,787
Other comprehensive income (loss)	(9,766)	15,943	(1,535)	20,933
Ending balance	642,772	600,346	642,772	600,346
Other Comprehensive Income (Loss) before Reclassifications, Tax			0	78
Reclassification to net income, tax expense			1	37
Total accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(117,349)	(135,460)	(117,349)	(135,460)
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,043)	(32,299)	(7,056)	(34,896)
OCI, before Reclassifications		13,777
Other comprehensive income (loss)	(11,969)	13,777	(5,956)	16,374
Ending balance	(13,012)	(18,522)	(13,012)	(18,522)
Pension and other post-retirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(106,543)	(119,239)	(108,760)	(121,448)
Reclassifications to net income:	2,203	2,159	4,420	4,368
Other comprehensive income (loss)	2,203	2,159	4,420	4,368
Ending balance	(104,340)	(117,080)	(104,340)	(117,080)
Amortization of net loss, net of tax expense	703	1,335	1,413	2,670
Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	3	135	2	(49)
OCI, before Reclassifications	0	8	0	129
Reclassifications to net income:	0	(1)	1	62
Other comprehensive income (loss)	0	7	1	191
Ending balance	3	142	$ 3	$ 142
Other Comprehensive Income (Loss) before Reclassifications, Tax	0	5
Reclassification to net income, tax expense	$ 0	$ 0