Dividends (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Dividends Payable [Line Items]
Dividends declared - per share	$ 0.48	$ 0.40	$ 0.96	$ 0.80
Dividends declared - aggregate	$ 9,863	$ 8,780	$ 20,061	$ 17,546
Common Stock, Dividends, Per Share, Cash Paid	$ 0.48	$ 0.40	$ 0.96	$ 0.80
Dividends paid - aggregate	$ 9,863	$ 8,780	$ 20,061	$ 17,546