Stock-Based Compensation (Details 2) (USD $)	3 Months Ended	1 Months Ended
Mar. 31, 2013 Restricted stock awards	Mar. 31, 2013 Performance share awards	Feb. 29, 2008 Executive Management Restricted stock awards
Stock-based compensation
Vesting period of shares awarded in 2008	3 years	3 years	5 years
Award Activity
Units granted (in shares)	10,808		56,700
Performance share awards
Shares granted (in dollars per share)		$ 91.33
Weighted average grant date fair value (in dollars per share)	$ 64.80

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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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