Earnings per share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 0	$ 5,227	$ 4,243
Weighted average common stock outstanding – basic		19,374,601	13,624,599
Stock options using the treasury method		884,583	897,628
Weighted average common stock outstanding – diluted		20,259,184	14,522,227
Stock options excluded from the calculation of diluted earnings per share because inclusion would have been anti-dilutive		0	0