Income taxes - Net Operating Loss Carryforwards (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income taxes
Net operating loss carryforwards	$ 56,800,000
Valuation allowance	928,701	$ 20,561,516	$ 28,500,000
Valuation allowance deferred tax asset change in amount	19,600,000
Net Operating Loss Deferred Tax Asset	$ 900,000