Long and short-term capital leases (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Long and short-term capital leases
Less: short-term portion capital leases	$ (166,966)	$ (290,911)
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.15% to 13.45%.
Long and short-term capital leases
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.15% to 13.45%. Principal and interest are payable monthly through September 2018	268,843	487,111
Total long and short-term portions of capital leases	268,843	487,111
Less: short-term portion capital leases	(166,966)	(290,911)
Long-term portion of capital leases	101,877	196,200
Total term debt interest expense	$ 28,668	$ 46,958	$ 61,591
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.15% to 13.45%. | Minimum
Long and short-term capital leases
Interest rate (as a percent)	4.15%
Capital leases to various lessors secured by financed equipment with interest rates ranging from 4.15% to 13.45%. | Maximum
Long and short-term capital leases
Interest rate (as a percent)	13.45%