Fair Value Measurements (Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Level 1 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure		$ 2,473
Financial Liabilities Fair Value Disclosure	$ 1,679	0
Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	39,256	37,807
Financial Liabilities Fair Value Disclosure	9,176	6,177
Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	39,256	40,280
Financial Liabilities Fair Value Disclosure	10,855	6,177
Foreign Exchange Forward [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	11,239	25,956
Foreign Exchange Forward [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	11,239	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	1,679
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	1,679
Commodity Contract [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	23,823	10,817
Financial Liabilities Fair Value Disclosure	14	956
Commodity Contract [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	23,823	10,817
Financial Liabilities Fair Value Disclosure	14	956
Forward Contracts [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	4,194	1,034
Financial Liabilities Fair Value Disclosure	3,933	1,137
Forward Contracts [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Assets Fair Value Disclosure	4,194	1,034
Financial Liabilities Fair Value Disclosure	3,933	1,137
Renewable Energy Program [Member] | Level 2 [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	5,229	4,084
Renewable Energy Program [Member] | Reported Value Measurement [Member]
Debt Instrument [Line Items]
Financial Liabilities Fair Value Disclosure	$ 5,229	$ 4,084