Income Taxes - Principal Components Of The Company's Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax assets:
Accruals not yet tax deductible	$ 142,100	$ 95,746
Pension and postretirement healthcare plan obligations	6,499	17,685
Stock compensation	9,619	11,867
Net operating loss and credit carryforwards	55,857	45,279
Valuation allowance	(38,072)	(29,024)
Other	78,051	64,833
Deferred tax assets, net	254,054	206,386
Deferred income tax liabilities:
Depreciation, tax in excess of book	(74,579)	(83,477)
Other	(29,544)	(29,840)
Deferred tax liabilities, net	(104,123)	(113,317)
Total	$ 149,931	$ 93,069