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
	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	7,321us-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	1,098us-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	1,955us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_RealizedGainsLossesMember / us-gaap_UnderlyingAssetClassAxis = us-gaap_CollateralizedSecuritiesOtherMember	14,997us-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	6,656us-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	66,456us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember	17,311us-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	3,916us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_CorporateBondSecuritiesMember	252us-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	20,565us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorSubordinatedNotesMember	36,955us-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	5,118us-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	$ 67,619us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FairValueByFairValueHierarchyLevelAxis = bx_NetChangeInUnrealizedGainsLossesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember	$ 15,059us-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

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