Fair Value Measurements And Derivative Instruments Fair Value Measurements And Derivative Instruments (Schedule Of Fair Value Of Derivatives) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivatives designated as cash flow hedges:
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 3,410	$ 350
Liability Derivatives	4,199	11,023
Derivatives designated as cash flow hedges: | Commodity derivative contracts | Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	104	90
Derivatives designated as cash flow hedges: | Commodity derivative contracts | Other accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	1,872	4,630
Derivatives designated as cash flow hedges: | Commodity derivative contracts | Other long-term assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	369	260
Derivatives designated as cash flow hedges: | Commodity derivative contracts | Other long-term obligations
Derivatives, Fair Value [Line Items]
Liability Derivatives	2,255	6,393
Derivatives designated as cash flow hedges: | Interest rate swap | Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	253
Derivatives designated as cash flow hedges: | Interest rate swap | Other accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	0
Derivatives designated as cash flow hedges: | Interest rate swap | Other long-term assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	2,684
Derivatives designated as cash flow hedges: | Interest rate swap | Other long-term obligations
Derivatives, Fair Value [Line Items]
Liability Derivatives	72
Derivatives not designated as hedges:
Derivatives, Fair Value [Line Items]
Asset Derivatives	615
Liability Derivatives	81
Derivatives not designated as hedges: | Commodity derivative contracts | Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	376
Derivatives not designated as hedges: | Commodity derivative contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	0
Derivatives not designated as hedges: | Foreign currency derivatives | Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	239	0
Derivatives not designated as hedges: | Foreign currency derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 81	$ 43