Derivative Financial Instruments (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gains or losses on derivative instruments, statement of income
Ineffectiveness - amount of gain (loss) recognized in income on related hedged items	$ 68,000	$ (28,000)	$ 85,000
Gain (loss) excluded from hedge effectiveness testing	(2,600,000)	(1,600,000)	2,700,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	2,800,000	137,000	544,000
Net gains (loss) reclassified	265,000	541,000	$ 149,000
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	2,500,000
Futures | Commodity contract | Other current assets
Commodity contract commitments
Fair value of derivatives including required margin deposits	$ 13,200,000	$ 3,700,000