Segment information (Details Textual) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Retail [Member]
Depreciation, Amortization and Accretion, Net	$ 508,259	$ 521,786	$ 1,018,899	$ 1,052,225
Bulk [Member]
Depreciation, Amortization and Accretion, Net	767,609	1,285,167	1,532,125	2,554,092
Services [Member]
Depreciation, Amortization and Accretion, Net	$ 73,181	$ 73,279	$ 146,363	$ 134,058