Earnings per share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Computation of basic and diluted earnings per share
Net income	$ 3,522	$ 3,353
Weighted average common shares outstanding - basic	88,246,000	87,436,000
Plus: net effect of dilutive stock options	181,000	336,000
Plus: net effect of dilutive restricted stock awards and units	197,000	163,000
Weighted average common shares outstanding, diluted (in shares)	88,624,000	87,935,000
Net income per common share-basic (in dollars per share)	$ 0.04	$ 0.04
Net income per common share-diluted (in dollars per share)	$ 0.04	$ 0.04
Stock Options
Computation of basic and diluted earnings per share
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)	2,940,897	1,434,314
Restricted Stock Units
Computation of basic and diluted earnings per share
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)	71,192	25,541