Benefit Plans (Summary Of Restricted Stock Activity) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Time-Based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares, Jan. 1	70,033	125,349	156,807
Granted, Shares	5,000		51,236
Vested, Shares	(38,633)	(54,016)	(79,459)
Forfeited, Shares	(600)	(1,300)	(3,235)
Nonvested shares, Dec. 31	35,800	70,033	125,349
Nonvested shares, Jan. 1, Weighted Average Fair Value	$ 32.27	$ 32.47	$ 32.80
Granted, Weighted Average Fair Value	$ 39.86		$ 29.40
Vested, Weighted Average Fair Value	$ 34.60	$ 32.72	$ 31.08
Forfeited, Weighted Average Fair Value	$ 29.41	$ 32.78	$ 33.97
Nonvested shares, Dec. 31, Weighted Average Fair Value	$ 30.87	$ 32.27	$ 32.47
Performance-Contingent Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares, Jan. 1	296,190	226,007	124,185
Granted, Shares	64,217	72,487	101,822
Vested, Shares	(53,274)
Forfeited, Shares	(5,395)	(2,304)
Nonvested shares, Dec. 31	301,738	296,190	226,007
Nonvested shares, Jan. 1, Weighted Average Fair Value	$ 32.32	$ 32.25	$ 39.28
Granted, Weighted Average Fair Value	$ 38.75	$ 32.56	$ 23.67
Vested, Weighted Average Fair Value	$ 37.93
Forfeited, Weighted Average Fair Value	$ 38.00	$ 32.56
Nonvested shares, Dec. 31, Weighted Average Fair Value	$ 32.60	$ 32.32	$ 32.25