Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Gains or losses on derivative instruments, statement of income
Ineffectiveness - amount of gain (loss) recognized in income on related hedged items	$ (61,000)	$ (1,100,000)
Gain (loss) excluded from hedge effectiveness testing	1,400,000	(2,200,000)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	11,000	58,000
Net gains (loss) reclassified	(37,000)	$ 283,000
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	$ 39,000
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	$ 2,600,000		$ 3,700,000