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Stock-Based Compensation Plans (Details 3) (USD $)	12 Months Ended
Stock-Based Compensation Plans (Details 3) (USD $)	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of performance of share activity
Share pay-out at plan, net of forfeitures of 14,563 for 2011	63,102	87,035	137,778
Actual share pay-out in following year	94,653	130,552	206,664
Performance Shares [Member]
Summary of performance of share activity
Fair value per share on grant date	21.56	14.29	7.94

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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