Basic and diluted net income per common share (Schedule of Earnings Per Share Reconciliation) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 5,918	$ 4,089	$ 4,824	$ 1,940	$ 5,567	$ 5,099	$ 4,795	$ 5,118	$ 16,771	$ 20,579	$ 3,737
Weighted-average shares outstanding - basic (in shares)									71,895,427	71,788,827	62,265,230
Dilutive securities (in shares)									263,755	179,926	74,640
Weighted-average shares outstanding - diluted (in shares)									72,159,182	71,968,753	62,339,870
Common stock equivalent shares excluded due to antidilutive effect (in shares)									450	3,361,624	85,901
Earnings Per Share, Basic and Diluted [Abstract]
Net income per common share (basic) (in dollars per share)	$ 0.08	$ 0.06	$ 0.07	$ 0.03	$ 0.08	$ 0.07	$ 0.07	$ 0.07	$ 0.23	$ 0.29	$ 0.06
Net income per common share (diluted) (in dollars per share)	$ 0.08	$ 0.06	$ 0.07	$ 0.03	$ 0.08	$ 0.07	$ 0.07	$ 0.07	$ 0.23	$ 0.29	$ 0.06