Earnings per Share (Reconciliation of Denominator for Basic and Diluted Earnings Per Share) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Abstract]
Basic	66,311,958	66,012,102	66,240,225	65,919,892
Plus incremental shares from: Assumed exercise of options	344,802	369,830	381,295	387,712
Weighted average common shares-diluted	66,656,760	66,381,932	66,621,520	66,307,604
Earnings per share: Basic	$ 1.30	$ 1.02	$ 4.36	$ 3.50
Earnings per share: Diluted	$ 1.30	$ 1.01	$ 4.33	$ 3.48