Fair Value Measurements (Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Level 1 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	$ 2,976	$ 2,473
Financial Liabilities Fair Value Disclosure	0	0
Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	21,971	37,807
Financial Liabilities Fair Value Disclosure	2,478	6,177
Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	24,947	40,280
Financial Liabilities Fair Value Disclosure	2,478	6,177
Nymex Futures Contracts [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure		2,473
Nymex Futures Contracts [Member] | Level 1 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	2,976	2,473
Nymex Futures Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	2,976
Foreign Exchange Forward [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	2,511	25,956
Financial Liabilities Fair Value Disclosure	17
Foreign Exchange Forward [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	2,511	25,956
Financial Liabilities Fair Value Disclosure	17
Commodity Contract [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	18,007	10,817
Financial Liabilities Fair Value Disclosure	1,094	956
Commodity Contract [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	18,007	10,817
Financial Liabilities Fair Value Disclosure	1,094	956
Forward Contracts [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	1,453	1,034
Financial Liabilities Fair Value Disclosure	1,367	1,137
Forward Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	1,453	1,034
Financial Liabilities Fair Value Disclosure	$ 1,367	1,137
Renewable Energy Program [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure		4,084
Renewable Energy Program [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure		$ 4,084