Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Common Share (Details) [Abstract]
Number of anti-dilutive stock options	744,640	1,839,225	2,964,778
Earnings Per Common Share (Table Details) [Abstract]
Net earnings	$ 164,637	$ 171,642	$ 167,855
Basic weighted average shares	61,188,000	65,104,000	65,986,000
Effect of dilutive stock options	701,000	799,000	581,000
Diluted weighted average shares	61,889,000	65,903,000	66,567,000
Basic earnings per common share	$ 2.69	$ 2.64	$ 2.54
Diluted earnings per common share	$ 2.66	$ 2.60	$ 2.52