Income Taxes (Components of Deferred Income Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets:
Pension	$ 8,108	$ 11,799
Non-pension post-retirement benefits	13,385	22,810
Other accrued liabilities	13,213	19,244
Receivables	2,118	2,756
Net operating loss and charitable contribution carry forward	16,599	16,861
Tax credits	13,288	11,502
Total deferred income tax assets	66,711	84,972
Valuation allowance	(19,076)	(13,773)
Net deferred income tax assets	47,635	71,199
Deferred income tax liabilities:
Property, plant and equipment	18,246	23,921
Inventories	1,639	3,866
Intangibles and other	4,708	5,255
Total deferred income tax liabilities	24,593	33,042
Net deferred income tax asset	$ 23,042	$ 38,157