Earnings Per Common Share Computations (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 57,333	$ 50,309	$ 56,633	$ 51,398
Participating Securities, Distributed and Undistributed Earnings	(674)	(1,170)	(668)	(1,198)
Numerator for basic earnings from continuing operations per common share	56,659	49,139	55,965	50,200
Net earnings and comprehensive income	57,333	50,298	56,633	51,356
Net earnings allocated to participating securities	(674)	(1,170)	(668)	(1,198)
Numerator for basic net earnings per common share	56,659	49,128	55,965	50,158
Income Loss From Continuing Operations, Diluted	57,333	50,298	56,633	51,398
Net Income (Loss) Available to Common Stockholders, Diluted	$ 57,333	$ 50,298	$ 56,633	$ 51,356
Earnings Per Share, Basic and Diluted [Abstract]
Basic (in shares)	17,531	17,268	17,475	17,239
Plus dilutive effect of stock options (in shares)	140	242	200	232
Plus dilutive effect of participating securities (in shares)	209	411	209	411
Diluted (in shares)	17,880	17,921	17,884	17,882
Net earnings (in dollars per share), Basic	$ 3.23	$ 2.85	$ 3.20	$ 2.91
Net earnings (in dollars per share), Diluted	$ 3.21	$ 2.81	$ 3.17	$ 2.87