ShareBased Compensation Plans Performance Based Restricted Stock Units (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
PBRSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested Restricted Stock Units Outstanding, Beginning of Period	988,000	364,000
PBRSUs granted		227,860
PBRSUs Forfeited		(111,000)
Unvested Restricted Stock Units Outstanding, End of Period		988,000	364,000
Unvested Restricted Stock Units Outstanding, Beginning Balance	$ 17.71	$ 18.76
PBRSUs granted		$ 16.32
PBRSUs Forfeited		$ 18.47
Unvested Restricted Stock Units Outstanding Ending Balance		$ 17.71	$ 18.76
Performance Based Resrticted Stock Units Shares Issued			366,154
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	$ 3.7		$ 6.9
Unrecognized Compensation Costs Related To Restricted Stock Units		13.0
Total Compensation Cost Not yet Recognized, Period for Recognition (years)		2.6
Dorado PBRSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PBRSUs granted		506,736
PBRSUs granted		$ 17.76
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures		$ 9.0

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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- Definition

The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

The weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect during the reporting period as a result of the occurrence of a terminating event specified in the contractual agreement of the plan.

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- Definition

The number of grants made 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).

+ References

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph A240

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- Definition

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.

+ References

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-Paragraph A240

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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

Number of shares issued during the period related to Restricted Stock Awards, net of any shares forfeited.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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Value of stock related to Restricted Stock Awards issued during the period, net of the stock value of such awards forfeited.

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