Share - Based Compensation (Details 2) (Performance Share Units [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2012
Performance Share Units [Member]
Performance share units
Outstanding at the beginning of year, nonvested	859
Grants in periods, number of shares	535
Forfeited RSU's, number of shares	(53)
Outstanding at the end of year, nonvested	1,341
Outstanding at the beginning of year, weighted average grant date fair value	$ 22.98
Grants in periods, weighted average grant date fair value	$ 27.76
Forfeited in period, weighted average grant date fair value	$ (22.62)
Outstanding at the end of year, weighted average grant date fair value	$ 24.90

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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