Income Taxes - Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets:
Accrued liabilities	$ 44,541	$ 54,906
Retirement plans and postretirement benefits	10,751	12,190
Share-based compensation	452	2,343
Receivables and inventories	7,182	6,789
Derivative financial instruments	198	1,075
Net operating loss carryforwards	137,138	61,009
Tax credits and other carryforwards	32,707	23,195
Lease liability	72,907	0
Valuation allowances	(155,841)	(40,966)
Deferred income tax assets	150,035	120,541
Deferred income tax liabilities:
Property, plant and equipment	(74,247)	(113,272)
Operating lease right of use assets	(69,340)	0
Intangible assets	(5,603)	(14,475)
Prepaid expenses	(5,002)	0
Other	(909)	(3,983)
Deferred income tax liabilities	(155,101)	(131,730)
Net deferred income tax asset (liability)	(5,066)	(11,189)
Deferred tax assets related to uncertain tax positions	$ 4,400	$ 5,400