Income Taxes - Principal Components Of The Company's Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets:
Accruals not yet tax deductible	$ 95,746	$ 108,284
Pension and postretirement healthcare plan obligations	17,685	48,347
Stock compensation	11,867	13,295
Net operating loss carryforward	45,279	34,842
Valuation allowance	(29,024)	(21,868)
Other, net	64,833	43,870
Deferred tax assets, net	206,386	226,770
Deferred income tax liabilities:
Depreciation, tax in excess of book	(83,477)	(79,326)
Other	(29,840)	(5,980)
Deferred tax liabilities, net	(113,317)	(85,306)
Total	$ 93,069	$ 141,464