Stock-Based Compensation And Directors Stock Purchase Plan (Schedule Of Nonvested Share Awards) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011
Stock-Based Compensation And Directors Stock Purchase Plan [Abstract]
Nonvested share awards, beginning balance	493,847
Granted	218,631
Vested	(42,412)
Forfeited	(16,284)
Nonvested share awards, ending balance	653,782
Nonvested share awards, weighted average grant date fair value, beginning of period	$ 34.29
Granted	$ 38.50
Vested	$ 37.47
Forfeited	$ 33.87
Nonvested share awards, weighted average grant date fair value, end of period	$ 35.48