Fair Value Measurements (Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Level 1 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure		$ 2,473
Financial Liabilities Fair Value Disclosure	$ 2,645	0
Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	20,868	37,807
Financial Liabilities Fair Value Disclosure	5,038	6,177
Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	20,868	40,280
Financial Liabilities Fair Value Disclosure	7,683	6,177
Foreign Exchange Forward [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	1,553	25,956
Foreign Exchange Forward [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	1,553	25,956
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		2,473
Financial Liabilities Fair Value Disclosure	2,645
Nymex Futures Contracts [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	0
Nymex Futures Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	2,645
Commodity Contract [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	20,412	10,817
Financial Liabilities Fair Value Disclosure		956
Commodity Contract [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	20,412	10,817
Financial Liabilities Fair Value Disclosure		956
Forward Contracts [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	456	1,034
Financial Liabilities Fair Value Disclosure		1,137
Forward Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	456	1,034
Financial Liabilities Fair Value Disclosure		1,137
Renewable Energy Program [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	3,485	4,084
Renewable Energy Program [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	$ 3,485	$ 4,084