Earnings per share - Basic and Diluted (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 1,648,286	$ 921,630	$ 3,097,138	$ 2,058,493
Weighted average common shares outstanding	8,216,567	5,820,342	7,872,609	5,813,915
Effect of dilutive stock options (in shares)	108,971	311,478	104,673	304,615
Diluted shares	8,325,538	6,131,820	7,977,282	6,118,530
Basic earnings per common share (in dollars per share)	$ 0.20	$ 0.16	$ 0.39	$ 0.35
Diluted earnings per common share (in dollars per share)	$ 0.20	$ 0.15	$ 0.39	$ 0.34