Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Foreign operating loss carryforwards	$ 36,631	$ 35,394
Pension and other benefit programs	41,968	39,633
Foreign tax credit carryforwards	12,306	11,423
Accrued liabilities	12,883	10,726
Other credit carryforwards	8,639	6,707
Disallowed interest	7,692	2,633
Other	7,217	8,528
State and local operating loss carryforwards	1,900	2,058
Inventories	2,879	2,366
Allowance for doubtful accounts	589	746
Currency differences	5,605	1,407
Total deferred tax assets	138,309	121,621
Deferred tax liabilities:
Property, plant and equipment and intangibles -- depreciation and amortization	16,024	23,617
Unremitted earnings of foreign subsidiaries	1,903	1,594
Deferred gain	2,351	99
Other	2,030	2,016
Total deferred tax liabilities	22,308	27,326
Net deferred tax assets before valuation allowance	116,001	94,295
Valuation allowance	(10,872)	(10,447)
Net deferred tax assets	$ 105,129	$ 83,848