Derivative Instruments and Hedging Activities (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2011
Derivative [Line Items]
Remaining forward starting swaps settled	$ 20.0
Payment to counterparty for settled forward starting swaps	2.3
Derivatives net liability	1.6
Not Designated as Hedging Instrument [Member] \| Swap [Member]
Derivative [Line Items]
Amount of hedged item	38.0
Notional amount fixed spread basis	35.2
Term of swap (in years)	3
Notional amount fixed spread ratably increases over term of swap	38.0
Percentage of price depreciation the Company obligated to pay if bonds decline in value (in hundredths)	100.00%
Percentage of price appreciation Citibank obligated to pay if bonds increase in value (in hundredths)	85.00%
Fair value of the swap	1.6
Designated as Hedging Instrument [Member] \| Interest Rate Cap [Member]
Derivative [Line Items]
Number of interest rate cap contracts	12
Interest rate cap contracts notional amount	191.9
Tax exempt variable rate debt	202.9
Aggregate carrying value of the interest rate cap contracts	0.1
Accumulated Other Comprehensive Income (Loss) [Member]
Derivative [Line Items]
Change in fair value of derivatives	$ 4.0

Amount of the increase or decrease in fair value during the period of the hedged item recorded in accumulated other comprehensive income.

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- Definition

The length of the term of the swap.

+ Details

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- Definition

This item represents the fixed spread on the notional amount maximum amount.

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- Definition

Percentage obligated to pay if bonds decline in value from the estimated value at inception of the swap.

+ Details

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- Definition

Percentage obligated to pay if bonds increase in value from the estimated value at inception of the swap.

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- Definition

Notional amount of forward starting swaps settled.

+ Details

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- 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

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

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-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

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- Definition

Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 4B

-Subparagraph (a),(c)

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-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

Fair value as of the balance sheet date of the gross assets less the gross liabilities of a derivative liability or group of derivative liabilities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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-Paragraph 15

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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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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

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- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ Details

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- Definition

Aggregate notional amount of interest rate derivatives, which relates to the currency amount specified in the interest rate derivative instruments.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Aggregate notional amount of all derivatives not designated as a hedging instrument. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

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

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- Definition

The cash outflow for derivative instruments during the period, which are classified as investing activities, excluding those designated as hedging instruments.

+ Details

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