Inventories (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory [Line Items]
Inventory valuation adjustment	$ 455,000	$ 0	$ 2,590,000
Disposal Group, Including Discontinued Operation, Inventory, Current	15,600,000
Crude Supply and Logistics [Member] | Crude Oil [Member]
Inventory [Line Items]
Inventory valuation adjustment	$ 500,000