XML 69 R61.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Significant Transactions (Sale of Esurance) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended | 1 Months Ended
--- | --- | ---
Dec. 31, 2011 | Oct. 31, 2011 Esurance
Significant Transactions |  |
Consideration in excess of tangible book value |  | $ 700.0
Net gain on sale of discontinued operation - Esurance | $ 700.0 | $ 677.5

X
- Definition Consideration in excess of tangible book value for the sale of a business + References No definition available. + Details
Name: | wtm_ConsiderationInExcessOfTangibleBookValueForSaleOfBusiness
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the after-tax gain for the sale of a business. + References No definition available. + Details
Name: | wtm_DiscontinuedOperationGainOnDisposalOfDiscontinuedOperationNetOfTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | wtm_SignificantTransactionsLineItems
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration