Share-Based Payments (Details 1) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of activity for stock options
Stock Options, Outstanding, Beginning of the year	1,014,661	1,430,105	2,031,754
Stock Options, Outstanding, Granted	0	0	0
Stock Options, Outstanding, Exercised	(994,148)	(412,695)	(601,649)
Stock Options, Outstanding, Forfeited or Expired	(211)	(2,749)	0
Stock Options, Outstanding, Ending of the year	20,302	1,014,661	1,430,105
Stock Options, Outstanding, Exercisable at end of year	20,302	959,889	1,258,492
Stock Options, Outstanding at end of year, Vested or Expected to Vest	20,302	1,014,064	1,427,301
Summary of activity for stock options, weighted average exercise price
Stock Options, Outstanding, Weighted Average Exercise Price, Beginning of the year	$ 22.76	$ 21.85	$ 20.17
Stock Options, Outstanding, Weighted Average Exercise Price, Granted	$ 0.00	$ 0.00	$ 0.00
Stock Options, Outstanding, Weighted Average Exercise Price ,Exercised	$ 22.75	$ 19.61	$ 16.18
Stock Options, Outstanding, Weighted Average Exercise Price, Forfeited and Expired	$ 25.67	$ 25.36	$ 0.00
Stock Options, Outstanding, Weighted Average Exercise Price, End of the Period	$ 23.15	$ 22.76	$ 21.85
Stock Options, Outstanding, Weighted Average Exercise Price, Exercisable	$ 23.15	$ 22.59	$ 21.40
Stock Options, Outstanding at end of year, Weighted Average Exercise Price, vested or expected to vest	$ 23.15	$ 22.75	$ 21.85

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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