Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Income Taxes [Line Items]
Income tax benefit	$ 10,862	$ (1,591)
Pension settlement charge	42,988
Pension Plans [Member]
Income Taxes [Line Items]
Income tax benefit	11,200
Increase in deferred tax assets	6,800
Remeasurement of pension plan obligations	26,200
Deltic MDF Facility [Member]
Income Taxes [Line Items]
Reduction to deferred tax liabilities	(15,800)
Increase to income taxes payable	$ 15,800

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109238882&loc=d3e38679-109324

Name:	us-gaap_IncomeTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration