Segment information (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Retail [Member]
Segment Reporting Information [Line Items]
Depreciation, Depletion and Amortization	$ 598,079	$ 598,223	$ 1,204,668	$ 1,231,496
Bulk [Member]
Segment Reporting Information [Line Items]
Depreciation, Depletion and Amortization	792,241	780,510	1,570,418	1,566,412
Services [Member]
Segment Reporting Information [Line Items]
Depreciation, Depletion and Amortization	$ 22,474	$ 22,474	$ 44,948	$ 57,448