Share-Based Compensation Arrangements (Nonvested Share Units Activity) (Details) (Time Based Nonvested Shares [Member], USD $)	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Time Based Nonvested Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options	108,775		91,250
Equity Instruments Other than Options Weighted Average Grant Date Fair Value	$ 20.82		$ 19.84
Equity Instruments Other than Options Granted	29,725	31,950
Equity Instruments Other than Options Granted Weighted Average Grant Date Fair Value	$ 23.62
Equity Instruments Other than Options Vested	(6,752)
Equity Instruments Other than Options Vested Weighted Average Grant Date Fair Value	$ 19.37
Equity Instruments Other than Options Forfeited	(5,448)
Equity Instruments Other than Options Forfeited Weighted Average Grant Date Fair Value	$ 21.54

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 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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- Definition

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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