Earnings Per Common Share (Computation 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, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Common Share [Abstract]
Income available to common stockholders and holders of dilutive securities	$ 44,555	$ 43,614	$ 42,765	$ 46,377	$ 46,071	$ 45,452	$ 46,415	$ 43,636	$ 177,311	$ 181,574	$ 136,096
Weighted average shares									89,678	95,295	102,114
Effect of dilutive securities: Stock options and stock awards									2,256	1,835	632
Adjusted weighted average shares									91,934	97,130	102,746
Per share amount, Basic	$ 0.52	$ 0.49	$ 0.46	$ 0.50	$ 0.49	$ 0.48	$ 0.48	$ 0.46	$ 1.98	$ 1.91	$ 1.33
Per share amount, Diluted	$ 0.51	$ 0.48	$ 0.45	$ 0.49	$ 0.48	$ 0.47	$ 0.47	$ 0.45	$ 1.93	$ 1.87	$ 1.32