Earnings per share - Basic and Diluted (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 3,931,556	$ 1,648,286	$ 7,346,326	$ 3,097,138
Weighted average common shares outstanding (in shares)	12,201,185	8,216,567	11,708,746	7,872,609
Effect of dilutive stock options (in shares)	119,313	108,971	113,751	104,673
Diluted shares (in shares)	12,320,498	8,325,538	11,822,497	7,977,282
Basic earnings per common share (in dollars per share)	$ 0.32	$ 0.20	$ 0.63	$ 0.39
Diluted earnings per common share (in dollars per share)	$ 0.32	$ 0.20	$ 0.62	$ 0.39