Benefit Plans (Summary Of Restricted Stock Activity) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Time-Based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	35,800		70,033		125,349
Nonvested shares, January 1, weighted average fair value (in dollars per share)	$ 30.87		$ 32.27		$ 32.47
Granted (in shares)	0		5,000		0
Granted, weighted average fair value (in dollars per share)	$ 0.00		$ 39.86		$ 0.00
Vested (in shares)	(32,466)		(38,633)		(54,016)
Vested, weighted average fair value (in dollars per share)	$ 29.95		$ 34.60		$ 32.72
Forfeited (in shares)	0		(600)		(1,300)
Forfeited, weighted average fair value (in dollars per share)	$ 0.00		$ 29.41		$ 32.78
Nonvested, December 31 (in shares/awards)	3,334		35,800		70,033
Nonvested shares, December 31, weighted average fair value (in dollars per share)	$ 39.86		$ 30.87		$ 32.27
Performance-Contingent Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	301,738		296,190		226,007
Nonvested shares, January 1, weighted average fair value (in dollars per share)	$ 32.60		$ 32.32		$ 32.25
Granted (in shares)	45,612		64,217		72,487
Granted, weighted average fair value (in dollars per share)	$ 43.05		$ 38.75		$ 32.56
Vested (in shares)	(65,172)	[1]	(53,274)	[1]	0	[1]
Vested, weighted average fair value (in dollars per share)	$ 32.56	[1]	$ 37.93	[1]	$ 0.00	[1]
Forfeited (in shares)	(70,527)	[2]	(5,395)	[2]	(2,304)	[2]
Forfeited, weighted average fair value (in dollars per share)	$ 39.93	[2]	$ 38.00	[2]	$ 32.56	[2]
Nonvested, December 31 (in shares/awards)	211,651		301,738		296,190
Nonvested shares, December 31, weighted average fair value (in dollars per share)	$ 32.42		$ 32.60		$ 32.32
Performance-Contingent Restricted Stock [Member] | Performace Criteria Not Met [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Forfeited (in shares)	(65,516)	[2]

[1] In 2012 and 2011, 65,172 and 53,274 performance-contingent restricted shares granted in 2010 and 2007, respectively, vested because the specified performance criteria for such shares were met.

[2] In 2012, 65,516 performance-contingent restricted shares granted in 2008 were forfeited because the specified performance criteria for such shares were not met. The remaining forfeitures during 2012, 2011 and 2010 were primarily caused by retirements and terminations of participants.