Shareholders Equity (Schedule Of Changes In Non-Vested Restricted Shares) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Shareholders' Equity
Non-vested shares at beginning of period, Number of Shares	664,909	466,387	327,751
Non-vested shares at end of period, Weighted Average Grant Price	$ 22.16	$ 22.29	$ 23.83
Shares granted, Number of Shares	276,869	233,460	162,507
Shares granted, Weighted Average Grant Price	$ 21.78	$ 21.83	$ 19.34
Shares vested, net of shares repurchased to cover tax withholding requirements,, Number of Shares	(208,949)	(8,973)	(9,666)
Shares vested, net of shares repurchased to cover tax withholding requirements, , Weighted Average Grant Price	$ 23.11	$ 20.45	$ 22.55
Shares forfeited, Number of Shares	(417)	(25,965)	(14,205)
Shares forfeited, Weighted Average Grant Price	$ 24.75	$ 22.21	$ 23.59
Non-vested shares at end of period, Number of Shares	732,412	664,909	466,387
Non-vested shares at end of period, Weighted Average Grant Price	$ 21.91	$ 22.16	$ 22.29