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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 5,567	$ 5,099	$ 4,795	$ 5,118	$ 5,040	$ 2,432	$ (4,678)	$ 943	$ 20,579	$ 3,737	$ 50,845
Weighted-average shares outstanding - basic (in shares)									71,788,827	62,265,230	47,186,756
Dilutive securities (in shares)									179,926	74,640	296,956
Weighted-average shares outstanding - diluted (in shares)									71,968,753	62,339,870	47,483,712
Common stock equivalent shares excluded due to antidilutive effect (in shares)									3,361,624	85,901	64,171
Earnings Per Share, Basic and Diluted [Abstract]
Net income per common share (basic) (in dollars per share)	$ 0.08	$ 0.07	$ 0.07	$ 0.07	$ 0.07	$ 0.03	$ (0.08)	$ 0.02	$ 0.29	$ 0.06	$ 1.08
Net income per common share (diluted) (in dollars per share)	$ 0.08	$ 0.07	$ 0.07	$ 0.07	$ 0.07	$ 0.00	$ 0.00	$ 0.00	$ 0.29	$ 0.06	$ 1.07