Derivative Instruments - (Details Textual) lb in Millions, gal in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) lb gal
Derivative Instruments, Gain (Loss) [Line Items]
Heating oil covered under the open commodity derivative contracts (in gallons) | gal	82.8
Soybean oil covered under the open commodity derivative contracts (in pounds) | lb	78.3
Net position	$ 7,189,000
Commodity contract derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Collateral associated with commodity-based derivatives	$ 8,798,000