Supplemental Balance Sheet Information Related to Leases (Details) - USD ($) $ in Thousands	Jun. 26, 2020	Dec. 31, 2019
Operating Leases
Operating lease right-of-use assets	$ 48,942	$ 23,413
Other liabilities and accrued items	5,298	6,542
Operating lease liabilities	44,830	18,091
Finance Leases
Finance lease liabilities	16,939	17,424
Total principal payable on finance leases	18,244	18,689
Property, plant, and equipment	924,620	916,965
Allowances for depreciation, depletion, and amortization	(685,355)	(684,689)
Finance lease assets, net	239,265	232,276
Other liabilities and accrued items	1,305	1,265
Property, Plant and Equipment
Property, plant, and equipment	26,258	26,069
Allowances for depreciation, depletion, and amortization	(4,035)	(3,570)
Finance lease assets, net	$ 22,223	$ 22,499