Derivative Financial Instruments (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gains or losses on derivative instruments, statement of income
Ineffectiveness - amount of gain (loss) recognized in income on related hedged items	$ (28,000)	$ 85,000	$ (3,000)
Gain (loss) excluded from hedge effectiveness testing	(1,600,000)	2,700,000	$ (938,000)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	137,000	544,000
Net gains reclassified	541,000	149,000
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	$ 9,600
Period Within Which The Company Expects To Reclassify Net Gains On Derivative Instruments From A O C I to Earnings	12 months
Futures | Commodity contract | Other current assets
Commodity contract commitments
Fair value of derivatives including required margin deposits	$ 3,700,000	$ 4,900,000