XML 25 R57.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Net Income (Loss) Attributable to Noncontrolling Interest | $ (7.3)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | $ (0.6)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest |
Private equity funds |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Other long-term investments | 150.4 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_PrivateEquityFundsMember |  |
1-3 years | Private equity funds |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Other long-term investments | 29.7 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_PrivateEquityFundsMember / wtm_PrivateEquityFundsRemainingLockUpPeriodAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriod1To3YearsMember |  |
3-5 years | Private equity funds |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Other long-term investments | 32.4 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_PrivateEquityFundsMember / wtm_PrivateEquityFundsRemainingLockUpPeriodAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriod3To5YearsMember |  |
5-10 years | Private equity funds |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Other long-term investments | 84.1 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_PrivateEquityFundsMember / wtm_PrivateEquityFundsRemainingLockUpPeriodAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriod5To10YearsMember |  |
Greater than 10 years | Private equity funds |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Other long-term investments | 4.2 us-gaap_TradingSecuritiesOther / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_PrivateEquityFundsMember / wtm_PrivateEquityFundsRemainingLockUpPeriodAxis = wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodOver10YearsMember |  |
Prospector Funds [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage | 68.00%us-gaap_VariableInterestEntityOwnershipPercentage / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember |  |
Equity Method Investment, Aggregate Cost | 64.7 us-gaap_EquityMethodInvestmentAggregateCost / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember |  | 64.9 us-gaap_EquityMethodInvestmentAggregateCost / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember
Variable Interest Entity, Consolidated, Carrying Amount, Assets | 136.1 us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember |  | 135.8 us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities | 40.4 us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember |  | 39.8 us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember
Net Income (Loss) Attributable to Noncontrolling Interest | $ 31.0 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember |  | $ 31.1 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = wtm_ProspectorFundsMember

X
- Definition This element represents the aggregate cost of investments accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 + Details
Name: | us-gaap_EquityMethodInvestmentAggregateCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of Net Income (Loss) attributable to noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=18733093&loc=SL4573702-111684 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4J -URI http://asc.fasb.org/extlink&oid=31814832&loc=SL4591551-111686 + Details
Name: | us-gaap_NetIncomeLossAttributableToNoncontrollingInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Amount of other investments classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.(a),1(c),(d),(e),(f),(g)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph c, d, e, f, g -Article 7 + Details
Name: | us-gaap_TradingSecuritiesOther
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685 + Details
Name: | us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685 + Details
Name: | us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=28200181&loc=SL6759159-111685 + Details
Name: | us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=wtm_ProspectorFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | wtm_PrivateEquityFundsRemainingLockUpPeriodAxis=wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriod1To3YearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | wtm_PrivateEquityFundsRemainingLockUpPeriodAxis=wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriod3To5YearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | wtm_PrivateEquityFundsRemainingLockUpPeriodAxis=wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriod5To10YearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | wtm_PrivateEquityFundsRemainingLockUpPeriodAxis=wtm_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodOver10YearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |