Income taxes (Details 1) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax expense	$ 1,371	$ 0
Deferred tax benefit	(890,348)	(536,057)
Income Tax Expense (Benefit)	$ (888,977)	$ (536,057)	$ 0