Basis of presentation - Schedule of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Basic earnings per common share calculation:
Net income	$ 745	$ 19,588
Dividends paid on and undistributed earnings allocated to participating securities	0	(105)
Earnings attributable to common shareholders	$ 745	$ 19,483
Weighted-average basic shares outstanding (in shares)	31,257,739	30,786,684
Basic earnings per common share (in dollars per share)	$ 0.02	$ 0.63
Diluted earnings per common share:
Earnings attributable to common shareholders	$ 745	$ 19,483
Weighted-average basic shares outstanding (in shares)	31,257,739	30,786,684
Weighted-average diluted shares contingently issuable (in shares)	476,373	562,514
Weighted-average diluted shares outstanding (in shares)	31,734,112	31,349,198
Diluted earnings per common share (in dollars per share)	$ 0.02	$ 0.62
Restricted stock units outstanding considered to be antidilutive (in shares)	153,545