Subsequent Events (Details) (USD $) In Millions, unless otherwise specified		1 Months Ended	9 Months Ended
Oct. 31, 2011 Interest rate cap contracts 2018 Notes Additional fixed-to-float interest rate swap	Oct. 31, 2011 Interest rate cap contracts 2020 Notes Additional fixed-to-float interest rate swap	Oct. 31, 2011 Additional fixed-to-float interest rate swap	Sep. 30, 2011 Interest rate cap contracts
Subsequent Events
Notional value of derivative	$ 75.0	$ 100.0
Amount of debt hedged	$ 200.0	$ 300.0
Spreads added to variable rate basis (as a percent)	7.45%	6.02%
Variable rate basis			six-month LIBOR	LIBOR rate of 3.00%

- Definition

Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

+ Details

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- Definition

The percentage points added to the reference rate to compute the variable rate on the interest rate derivative.

+ Details

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- Definition

The reference rate for the variable rate of the interest rate derivative, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ Details

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- Definition

Aggregate notional amount of all derivatives. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

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