v2.4.1.9

Realized and Net Change in Unrealized Gains (Losses) on Financial Instruments on Financial Instruments on Which Fair Value Option was Elected (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Realized Gains (Losses) | Liabilities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments |  | $ (2,538)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_FairValueByLiabilityClassAxis = bx_LiabilitiesMember
Realized Gains (Losses) | Assets |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | 7,321 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember | (22,731)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember
Realized Gains (Losses) | Corporate Bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | (1,105)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_CorporateBondSecuritiesMember | 1,098 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_CorporateBondSecuritiesMember
Realized Gains (Losses) | Senior Secured Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments |  | (2,538)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorNotesMember
Realized Gains (Losses) | Other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | 1,955 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_UnderlyingAssetClassAxis = us-gaap_CollateralizedSecuritiesOtherMember | 14,997 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_UnderlyingAssetClassAxis = us-gaap_CollateralizedSecuritiesOtherMember
Realized Gains (Losses) | Equity and Preferred Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | (185)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember | (584)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Realized Gains (Losses) | Corporate Loans |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | 6,656 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | (38,242)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Net Change In Unrealized Gains (Losses) | Liabilities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | (7,506)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_FairValueByLiabilityClassAxis = bx_LiabilitiesMember | (18,919)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_FairValueByLiabilityClassAxis = bx_LiabilitiesMember
Net Change In Unrealized Gains (Losses) | Assets |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | 66,456 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember | 17,311 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember
Net Change In Unrealized Gains (Losses) | Corporate Bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | 3,916 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_CorporateBondSecuritiesMember | 252 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_CorporateBondSecuritiesMember
Net Change In Unrealized Gains (Losses) | Senior Secured Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | (28,071)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorNotesMember | (55,874)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorNotesMember
Net Change In Unrealized Gains (Losses) | Subordinated Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | 20,565 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorSubordinatedNotesMember | 36,955 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorSubordinatedNotesMember
Net Change In Unrealized Gains (Losses) | Other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | (376)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_UnderlyingAssetClassAxis = us-gaap_CollateralizedSecuritiesOtherMember | (3,118)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_UnderlyingAssetClassAxis = us-gaap_CollateralizedSecuritiesOtherMember
Net Change In Unrealized Gains (Losses) | Loans And Receivables |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | (1,875)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = bx_LoansAndReceivablesMember |
Net Change In Unrealized Gains (Losses) | Equity and Preferred Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | (2,828)us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember | 5,118 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Net Change In Unrealized Gains (Losses) | Corporate Loans |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Realized and net change in unrealized gains (losses) on financial instruments | $ 67,619 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | $ 15,059 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember

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- Definition For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612 + Details
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