Earnings per share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 30, 2012	Sep. 30, 2013	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 0	$ 13,709	$ 17,952
Weighted average common stock outstanding – basic		25,078,727	17,484,598
Stock options using the treasury method		870,566	888,607
Weighted average common stock outstanding – diluted		25,949,293	18,373,205
Earnings per basic share		$ 0.55	$ 1.03
Earnings per diluted share		$ 0.53	$ 0.98
Stock options excluded from the calculation of diluted earnings per share because inclusion would have been anti-dilutive		0	0