Earnings per share - Basic and Diluted (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 1,684,869	$ 1,340,892	$ 4,782,007	$ 3,399,385
Weighted average common shares outstanding	8,234,783	5,834,520	7,994,661	5,820,834
Effect of dilutive stock options (in shares)	97,897	261,813	91,685	271,201
Diluted shares	8,332,680	6,096,333	8,086,346	6,092,035
Basic earnings per common share (in dollars per share)	$ 0.20	$ 0.23	$ 0.60	$ 0.58
Diluted earnings per common share (in dollars per share)	$ 0.20	$ 0.22	$ 0.59	$ 0.56