Supplemental Balance Sheet Information Related to Leases (Details) - USD ($) $ in Thousands	Jun. 28, 2019	Dec. 31, 2018
Operating Leases
Operating lease, right-of-use asset	$ 26,788	$ 0
Operating Lease, Liability, Current	6,927
Operating lease liabilities	21,118	0
Finance Leases
Finance lease liabilities	18,325	15,221
Total principal payable on finance lease	19,563
Property, Plant and Equipment	913,325	898,251
Allowance for depreciation, depletion and amortization	(669,861)	(647,233)
Finance lease assets, net	243,464	$ 251,018
Other liabilities and accrued items	1,238
Property, Plant and Equipment [Member]
Property, Plant and Equipment	26,330
Allowance for depreciation, depletion and amortization	(3,140)
Finance lease assets, net	$ 23,190