Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Gains or losses on derivative instruments, statement of income
Ineffectiveness - amount of gain (loss) recognized in income on related hedged items	$ 69,000	$ 5,000	$ 101,000	$ (10,500)
Gain (loss) excluded from hedge effectiveness testing	(399,000)	(2,100,000)	(918,000)	1,200,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	(8,000)	$ 82,000	139,000	$ (55,000)
Net gains reclassified	(43,000)		(483,000)
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	51,000		$ 51,000
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	$ 4,300,000		$ 4,300,000		$ 4,900,000