Fair Value Measurements (Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Level 1 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	$ 8,854	$ 3,360
Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	6,840	12,375
Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	15,694	15,735
Foreign Exchange Forward [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	9,137
Foreign Exchange Forward [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	9,137
Nymex Futures Contracts [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure		3,360
Nymex Futures Contracts [Member] | Level 1 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	8,854	3,360
Nymex Futures Contracts [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	0	0
Nymex Futures Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	8,854
Commodity Contract [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	1,565
Financial Liabilities Fair Value Disclosure	1,615	2,424
Commodity Contract [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	1,565
Financial Liabilities Fair Value Disclosure	1,615	2,424
Forward Contracts [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	4	1,020
Forward Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	4	1,020
Renewable Energy Program [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	5,221	8,931
Renewable Energy Program [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	5,221	8,931
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	10,727	3,840
Fair Value, Measurements, Recurring [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	10,727	3,840
Fair Value, Measurements, Recurring [Member] | Forward Contracts [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	25	3,840
Fair Value, Measurements, Recurring [Member] | Forward Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	$ 25	$ 3,840