Earnings per share - Basic and Diluted (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 4,731,249	$ 3,414,771
Weighted average common shares outstanding (in shares)	13,942,016	11,210,836
Effect of dilutive stock options (in shares)	76,147	108,858
Diluted shares (in shares)	14,018,163	11,319,694
Basic earnings per common share (in dollars per share)	$ 0.34	$ 0.30
Diluted earnings per common share (in dollars per share)	$ 0.34	$ 0.30