Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45014-112735

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)

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- Definition

Amount of minimum lease payments maturing in the next fiscal year following the latest fiscal year for capital leases.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)

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Amount of minimum lease payments maturing in the forth fiscal year following the latest fiscal year for capital leases.

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Amount of minimum lease payments maturing in the third fiscal year following the latest fiscal year for capital leases.

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Amount of minimum lease payments maturing in the second fiscal year following the latest fiscal year for capital leases.

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The liability as of the balance sheet date representing required funding mandated by statute or regulatory authority that is related directly or indirectly to underwriting activities, including pools for self-insurance and excluding premium taxes and income taxes. The funds derived from the assessments generally enable a government guarantor to pay insurance claims in the event that the underwriting insurer is insolvent or otherwise unable to meet its payment obligations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 405

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=9154593&loc=d3e23169-109297

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-Paragraph 1

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- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 1

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The gross proceeds received from the asset(s) sold in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller less the costs incurred in connection with the transaction, such as closing and deferred financing costs.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 40

-Section 55

-Paragraph 51

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-Paragraph 50

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Represents the period for which the assets have been acquired under the capital lease arrangement.

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No definition available.

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Represents the amount of binding commitments to fund other long-term investments.

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Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Rent expense	$ 19.4us-gaap_OperatingLeasesRentExpenseNet	$ 20.2us-gaap_OperatingLeasesRentExpenseNet	$ 18.8us-gaap_OperatingLeasesRentExpenseNet
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Capital lease payments due next year	16.5
Capital lease payments due in two years	15.2
Capital lease payments due in three years	13.6
Capital Lease payments due in four years and thereafter	54.7
Commitments to fund other-long term investments	81.7wtm_CommitmentsOtherLongTermInvestments
Reserve for probable liability from mandatory shared market mechanisms	11.9
OB Services
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Capital lease payments due next year	5.3
Capital lease payments due in two years	5.3
Capital lease payments due in three years	1.8
Cash proceeds received a result of entering into the sale-leaseback transactions	23.1
Capital lease obligation	7.1	12.5
Capital lease asset	$ 7.0	$ 10.9
Furniture and equipment \| OB Services
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Capital lease term (in years)	5 years
Capitalized software \| OB Services
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Capital lease term (in years)	4 years