Fair Value Measurements (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Dec. 31, 2011
Auction rate securities
1 year up to 20 years	$ 4.8
20 years up to 30 years	51.8
30 years up to 36 years	14.5
Investments in auction rate securities	71.1	70.9
Fair value assets measured on recurring basis unobservable input reconciliation calculation
Fair value, January 1, 2012	70.9
Unrealized gain included in other comprehensive loss	0.2
Fair value, March 31, 2012	$ 71.1

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The carrying value of auction rate securities maturing beyond a period of one year but within twenty years.

+ References

No definition available.

+ Details

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- Definition

The carrying value of auction rate securities maturing beyond a period of thirty years but within thirty six years.

+ References

No definition available.

+ Details

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- Definition

The carrying value of auction rate securities maturing beyond a period of twenty years but within thirty years.

+ References

No definition available.

+ Details

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- Definition

Total amount of investments in auction rate securities.

+ References

No definition available.

+ Details

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- Details

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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