Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 18,172	$ 17,692	$ 53,335	$ 49,764
Weighted average shares outstanding- basic and diluted (in shares)	5,113,077	5,111,201	5,112,108	5,110,435
Net income per common share- basic and diluted (in dollars per share)	$ 3.55	$ 3.46	$ 10.43	$ 9.74