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Stock-Based Compensation Plans (Details 3) (Performance Shares [Member], USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Performance Shares [Member]
Stock-based compensation expense
Share pay-out at plan, net of forfeitures of 14,563 for 2011	44,843	63,102	87,035
Actual share pay-out in following year	41,481	94,653	130,552
Fair value per share on grant date	$ 30.64	$ 21.56	$ 14.29

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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