Common Stock Plans (Performance Share Awards) (Details) (Performance Share Awards, Stock Incentive Plan, USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2010
Performance Share Awards \| Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Each unit of performance share awards equivalent to market value of number of common stock (shares)	1
Share-based compensation, vesting period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, Beginning of Period, Shares		111,143
Nonvested, Beginning of Period, Weighted Average Price		$ 43.81
Vested, Shares		(111,143)
Vested, Weighted Average Price		$ 43.81
Nonvested, End of Period, Shares		0
Nonvested, End of Period, Weighted Average Price		$ 0.00

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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