Related Parties (Details) (Director [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Related Party Transaction [Line Items]
Related Party Transaction Amount of Assets in Defined Contributions Plans	$ 20.4	$ 19.3	$ 18.2
Related Party Transaction Percent of Assets in Defined Contribution Plan Assets	7.00%	7.00%	6.00%
Trinity [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Assets Managed by Investment Advisory Firm under Director's Management	125.2
Related Party Transaction, Expenses from Transactions with Related Party	0.3	0.3	0.1
Pension Plans, Defined Benefit [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	0.3	0.3	0.3
Related Party Transaction Amount of Assets Under Management in Defined Benefit Plans	$ 120.7	$ 107.1	$ 98.3

Amounts Invested in Defined Contribution Plan Mutual Fund Managed by a Director's Investment Advisory Firm

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- Definition

Amounts Invested in Defined Contribution Plan Mutual Fund Managed by a Director's Investment Advisory Frim, Percentage of Total Defined Contribution Plan Investments

+ References

No definition available.

+ Details

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- Definition

Investment Assets Managed by a Directors Investment Advisory Firm

+ References

No definition available.

+ Details

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- Definition

Related Party Transaction Amount of Assets Under Management in Defined Benefit Plans

+ References

No definition available.

+ Details

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- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 2

-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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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