Summary Of Significant Accounting Policies (Calculation Of Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Basic earnings per common share, Income (Numerator)	$ 56,585	$ 50,743	$ 49,555	$ 49,965	$ 44,396	$ 49,232	$ 53,603	$ 57,728	$ 206,848	$ 204,959	$ 231,687
Basic earnings per common share, shares									174,295	182,547	188,468
Basic earnings per common share	$ 0.33	$ 0.29	$ 0.28	$ 0.28	$ 0.25	$ 0.27	$ 0.29	$ 0.31	$ 1.19	$ 1.12	$ 1.23
Dilutive effect of stock options, Income (Numerator)									0	0	0
Dilutive effect of stock options, Shares (Denominator)									1,577	1,580	1,853
Diluted earnings per common share, Income (Numerator)									$ 206,848	$ 204,959	$ 231,687
Diluted earnings per common share, shares									175,872	184,127	190,321
Diluted earnings per common share	$ 0.32	$ 0.29	$ 0.28	$ 0.28	$ 0.25	$ 0.27	$ 0.29	$ 0.31	$ 1.18	$ 1.11	$ 1.22