Earnings per share - Basic and Diluted (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 3,414,771	$ 1,448,851
Weighted average common shares outstanding (in shares)	11,210,836	7,524,830
Effect of dilutive stock options (in shares)	113,216	106,389
Diluted shares (in shares)	11,324,052	7,631,219
Basic earnings per common share (in dollars per share)	$ 0.30	$ 0.19
Diluted earnings per common share (in dollars per share)	$ 0.30	$ 0.19