Stock Based Compensation (Details Textuals) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Stock Based Compensation (Textuals) [Abstract]
Total fair value of vested stock options	$ 5,000,000		$ 4,000,000
Average cost per share, salary share	14.49		12.41
Number of highly compensated employees to be vested in future	20
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense for vesting of stock options	2,000,000	1,000,000	5,000,000
Unvested share-based payment awards	20,000,000
Total compensation cost not yet recognized, period for recognition	fourth quarter 2014
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested share-based payment awards	10,000,000
Total compensation cost not yet recognized, period for recognition	fourth quarter 2014
Expense for restricted stock awards	2,000,000	1,000,000	6,000,000
Salary Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense for vesting of stock options		$ 1,000,000	$ 4,000,000
Salary shares granted		60,992	317,450

Average cost per share, salary share.

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Employee service share based compensation nonvested awards total compensation cost not yet recognized year for recognition.

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Number of highly compensated employees to be vested in future.

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Share based compensation arrangement by share based payment award equity instruments options vested in period total fair value.

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No definition available.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

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The number of shares issued pursuant to the terms of the deferred compensation plan as of the balance sheet date.

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As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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