Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Common Share (Details) [Abstract]
Number of anti-dilutive stock options	1,115,245	744,640	1,839,225
Earnings Per Common Share (Table Details) [Abstract]
Net earnings	$ 183,492	$ 164,637	$ 171,642
Basic weighted average shares		61,188,000	65,104,000
Effect of dilutive stock options	492,000	701,000	799,000
Diluted weighted average shares		61,889,000	65,903,000
Basic earnings per common share	$ 3.11	$ 2.69	$ 2.64
Diluted earnings per common share	$ 3.09	$ 2.66	$ 2.60