Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of option activity and options exercisable including the weighted average exercise price
Options outstanding, Beginning balance	3,086,019	3,344,450	3,504,319
Options granted during the year	128,500	160,600	282,000
Options exercised during the year	(327,498)	(309,447)	(422,069)
Options terminated during the year	(48,468)	(109,584)	(19,800)
Options outstanding, Ending balance	2,838,553	3,086,019	3,344,450
Options exercisable at the Ending Period	2,322,258	2,306,159	2,148,100
Weighted Average Exercise Price, Beginning balance	$ 23.52	$ 22.80	$ 22.09
Weighted Average Exercise Price, Granted	$ 29.63	$ 27.41	$ 23.72
Weighted Average Exercise Price, Exercised	$ 17.95	$ 17.19	$ 17.78
Weighted Average Exercise Price, Terminated	$ 27.63	$ 25.01	$ 22.03
Weighted Average Exercise Price, Ending balance	$ 24.37	$ 23.52	$ 22.80
Weighted Average Exercise Price, Exercisable, Ending balance	$ 24.64	$ 24.43	$ 23.91