Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Gains or losses on derivative instruments, statement of income
Ineffectiveness - amount of gain (loss) recognized in income on related hedged items	$ 21,000	$ (61,000)
Gain (loss) excluded from hedge effectiveness testing	5,400,000	1,400,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	9,300,000	11,000
Net gains (loss) reclassified	4,400,000	$ (37,000)
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	$ 7,400,000
Period Within Which The Company Expects To Reclassify Net Gains On Derivative Instruments From AOCI to Earnings	12 months
Futures | Commodity contract | Other current assets
Commodity contract commitments
Fair value of derivatives including required margin deposits	$ 15,600,000		$ 13,200,000