Leasing Arrangements Supplemental Balance Sheet Information Related to Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Leases
Operating Lease, Right-of-Use Asset	$ 23,413	$ 0
Other liabilities and accrued items	6,542
Operating lease liabilities	18,091	0
Finance Leases
Finance lease liabilities	17,424	15,221
Total principal payable on finance leases	18,689
Property, plant, and equipment	916,965	898,251
Allowances for depreciation, depletion, and amortization	(684,689)	(647,233)
Finance lease assets, net	232,276	$ 251,018	$ 255,578
Other liabilities and accrued items	2,224
Property, Plant and Equipment [Member]
Property, plant, and equipment	26,069
Allowances for depreciation, depletion, and amortization	(3,570)
Finance lease assets, net	22,499
Other Liabilities [Member]
Other liabilities and accrued items	$ 1,265