Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Income from continuing operations									$ 76,907	$ 67,396	$ 54,663
Income from discontinued operations									0	529	2,252
Net income - basic and diluted	$ 23,572	$ 18,172	$ 17,341	$ 17,822	$ 18,161	$ 17,692	$ 16,828	$ 15,244	$ 76,907	$ 67,925	$ 56,915
Weighted average shares outstanding - basic and diluted (in shares)									5,112,352	5,110,628	5,109,055
Income from continuing operations (in dollars per share)									$ 15.04	$ 13.19	$ 10.70
Income from discontinued operations (in dollars per share)									0	0.10	0.44
Net income per common share- basic and diluted (in dollars per share)									$ 15.04	$ 13.29	$ 11.14