Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 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	$ (1,100,000)	$ (101,000)
Gain (loss) excluded from hedge effectiveness testing	(2,200,000)	$ 5,000,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	58,000
Net gains reclassified	283,000
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	$ 170,000
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	$ 3,700,000		$ 4,900,000