XML 22 R78.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Derivatives Forward Contracts (Details) (Forward Contracts [Member]) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |  |  |  | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2012 USD ($) Rating | Sep. 30, 2012 USD ($) Rating | Sep. 30, 2012 SEK | Jun. 30, 2012 USD ($) | Dec. 31, 2011 USD ($) | Sep. 30, 2012 United States of America, Dollars USD ($) | Sep. 30, 2012 United States of America, Dollars USD ($) | Sep. 30, 2012 United Kingdom, Pounds USD ($) | Sep. 30, 2012 United Kingdom, Pounds USD ($) | Sep. 30, 2012 Euro Member Countries, Euro USD ($) | Sep. 30, 2012 Euro Member Countries, Euro USD ($) | Sep. 30, 2012 Sweden, Kronor USD ($) | Sep. 30, 2012 Sweden, Kronor USD ($) | Sep. 30, 2012 Foreign Currency Gain (Loss) [Member] USD ($) | Sep. 30, 2012 Foreign Currency Gain (Loss) [Member] USD ($) | Sep. 30, 2012 Goldman Sachs [Member] USD ($) | Sep. 30, 2012 J P Morgan Chase [Member] USD ($) | Sep. 30, 2012 HSBS Bank plc [Member] USD ($) | Sep. 30, 2012 Royal Bank of Canada [Member] USD ($) | Sep. 30, 2012 Deutsche Bank [Member] USD ($)
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Exposure On Fair Value Of Over The Counter Derivative Instruments | $ 38.8 | [1] | $ 38.8 | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5.6 | [1] | $ 7.3 | [1] | $ 12.4 | [1] | $ 8.0 | [1] | $ 5.5 | [1]
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0 |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Notional Amount | 38.8 |  | 38.8 |  | 254.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | 0.3 |  | 0.3 |  |  |  |  | 0.4 | 0.4 | 0 | 0 | (0.1) | (0.1) | 0 | 0 | 0 | 0 |  |  |  |  |  |  |  |  |  |
Derivative, Fair Value, Net | 0.3 |  | 0.3 |  |  | 0 | 0 | 0.4 | 0.4 | 0 | 0 | (0.1) | (0.1) | 0 | 0 | 0 | 0 |  |  |  |  |  |  |  |  |  |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | $ 0 |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
S&P Credit Ratings | 22 |  | 22 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | (2) Collateral provided (held) calculated under master netting agreement.

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Net Increase or Decrease in the fair value of the derivative or group of derivatives included in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 + Details
Name: | us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Purchases that have taken place during the period in relation to derivative assets measured at fair value on a recurring basis. + References No definition available. + Details
Name: | wtm_FairValueDerivativesMeasuredOnRecurringBasisAssetPurchases
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Sales and settlements that have taken place during the period in relation to derivative assets measured at fair value on a recurring basis. + References No definition available. + Details
Name: | wtm_FairValueDerivativesMeasuredOnRecurringBasisAssetSalesAndSettlements
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that were not covered by collateral. + References No definition available. + Details
Name: | wtm_NetExposureOnFairValueOfOverCounterDerivativeInstruments
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the S&P creditworthiness heirarchy ratings used by the entity. + References No definition available. + Details
Name: | wtm_SpCreditRatings
Namespace Prefix: | wtm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant