Stock-Based Compensation (Schedule of Nonvested Share Awards) (Details) (USD $)	6 Months Ended
Jun. 30, 2011
Stock-Based Compensation
Nonvested share awards, beginning balance	470,406
Granted	198,459
Vested	(24,562)
Forfeited	(6,398)
Nonvested share awards, ending balance	637,905
Nonvested share awards, weighted average grant date fair value, beginning of period	$ 36.00
Granted	$ 40.62
Vested	$ 40.28
Forfeited	$ 37.33
Nonvested share awards, weighted average grant date fair value, end of period	$ 37.24

Nonvested Share Awards, Beginning and Ending Balances

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- Definition

Number of nonvested shares that were forfeited during the reporting period.

+ Details

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- Definition

Number of nonvested shares that were granted during the reporting period.

+ Details

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- Definition

Number of nonvested shares that vested during the reporting period

+ Details

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Nonvested Share Awards Vested In Period Weighted Average Grant Date Fair Value

+ Details

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Data Type:	us-types:perShareItemType
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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Nonvested Share Awards Weighted Average Grant Date Unit Fair Value

+ Details

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Period Type:	instant

- Definition

Share-Based Compensation, Forfeited, Nonvested Share Award, Weighted Average Grant Date Fair Value

+ Details

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- Definition

Share Based Compensation, Granted, Nonvested Share Award Weighted Average Grant Date Fair Value

+ Details

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Data Type:	us-types:perShareItemType
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Period Type:	duration

- Details

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