v2.4.1.9

Offsetting of Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition	$ 82,034bx_GrossAndNetAmountsOfAssetsPresentedInTheStatementOfFinancialCondition	$ 3,813bx_GrossAndNetAmountsOfAssetsPresentedInTheStatementOfFinancialCondition
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Assets	80,995bx_GrossAmountOfFinancialAndDerivativeAssetsNotOffsetInTheStatementOfFinancialConditionFinancialInstruments	1,132bx_GrossAmountOfFinancialAndDerivativeAssetsNotOffsetInTheStatementOfFinancialConditionFinancialInstruments
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received, Assets		352bx_CashCollateralReceived
Net Amount, Assets	1,039bx_AssetNetAmount	2,329bx_AssetNetAmount
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	99,551bx_GrossAndNetAmountsOfLiabilitiesPresentedInTheStatementOfFinancialCondition	38,560bx_GrossAndNetAmountsOfLiabilitiesPresentedInTheStatementOfFinancialCondition
Gross Amount Not Offset in the Statement of Financial Condition, Financial Instruments, Liabilities	88,261bx_GrossAmountOfLiabilitiesNotOffSetInStatementOfFinancialConditionFinancialInstruments	30,570bx_GrossAmountOfLiabilitiesNotOffSetInStatementOfFinancialConditionFinancialInstruments
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Pledged, Liabilities	8,713bx_CashCollateralPledged	7,893bx_CashCollateralPledged
Net Amount, Liabilities	2,577bx_LiabilityNetAmount	97bx_LiabilityNetAmount
Repurchase Agreements
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	87,085bx_GrossAndNetAmountsOfLiabilitiesPresentedInTheStatementOfFinancialCondition / us-gaap_InvestmentTypeAxis = us-gaap_RepurchaseAgreementsMember	29,907bx_GrossAndNetAmountsOfLiabilitiesPresentedInTheStatementOfFinancialCondition / us-gaap_InvestmentTypeAxis = us-gaap_RepurchaseAgreementsMember
Gross Amount Not Offset in the Statement of Financial Condition, Financial Instruments, Liabilities	86,616bx_GrossAmountOfLiabilitiesNotOffSetInStatementOfFinancialConditionFinancialInstruments / us-gaap_InvestmentTypeAxis = us-gaap_RepurchaseAgreementsMember	29,438bx_GrossAmountOfLiabilitiesNotOffSetInStatementOfFinancialConditionFinancialInstruments / us-gaap_InvestmentTypeAxis = us-gaap_RepurchaseAgreementsMember
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Pledged, Liabilities	469bx_CashCollateralPledged / us-gaap_InvestmentTypeAxis = us-gaap_RepurchaseAgreementsMember	469bx_CashCollateralPledged / us-gaap_InvestmentTypeAxis = us-gaap_RepurchaseAgreementsMember
Freestanding Derivatives
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition	2,406bx_GrossAndNetAmountsOfAssetsPresentedInTheStatementOfFinancialCondition / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember	3,290bx_GrossAndNetAmountsOfAssetsPresentedInTheStatementOfFinancialCondition / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Assets	1,645bx_GrossAmountOfFinancialAndDerivativeAssetsNotOffsetInTheStatementOfFinancialConditionFinancialInstruments / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember	1,132bx_GrossAmountOfFinancialAndDerivativeAssetsNotOffsetInTheStatementOfFinancialConditionFinancialInstruments / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received, Assets		352bx_CashCollateralReceived / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Net Amount, Assets	761bx_AssetNetAmount / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember	1,806bx_AssetNetAmount / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	12,058bx_GrossAndNetAmountsOfLiabilitiesPresentedInTheStatementOfFinancialCondition / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember	8,653bx_GrossAndNetAmountsOfLiabilitiesPresentedInTheStatementOfFinancialCondition / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Gross Amount Not Offset in the Statement of Financial Condition, Financial Instruments, Liabilities	1,645bx_GrossAmountOfLiabilitiesNotOffSetInStatementOfFinancialConditionFinancialInstruments / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember	1,132bx_GrossAmountOfLiabilitiesNotOffSetInStatementOfFinancialConditionFinancialInstruments / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Pledged, Liabilities	8,244bx_CashCollateralPledged / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember	7,424bx_CashCollateralPledged / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Net Amount, Liabilities	2,169bx_LiabilityNetAmount / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember	97bx_LiabilityNetAmount / us-gaap_DerivativeByNatureAxis = bx_FreestandingDerivativesMember
Reverse Repurchase Agreements
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition	79,628bx_GrossAndNetAmountsOfAssetsPresentedInTheStatementOfFinancialCondition / us-gaap_DerivativeByNatureAxis = bx_ReverseRepurchaseAgreementsMember
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments, Assets	79,350bx_GrossAmountOfFinancialAndDerivativeAssetsNotOffsetInTheStatementOfFinancialConditionFinancialInstruments / us-gaap_DerivativeByNatureAxis = bx_ReverseRepurchaseAgreementsMember
Net Amount, Assets	278bx_AssetNetAmount / us-gaap_DerivativeByNatureAxis = bx_ReverseRepurchaseAgreementsMember
Net Investment Hedges
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition		523bx_GrossAndNetAmountsOfAssetsPresentedInTheStatementOfFinancialCondition / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NetInvestmentHedgingMember
Net Amount, Assets		523bx_AssetNetAmount / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NetInvestmentHedgingMember
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	408bx_GrossAndNetAmountsOfLiabilitiesPresentedInTheStatementOfFinancialCondition / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NetInvestmentHedgingMember
Net Amount, Liabilities	$ 408bx_LiabilityNetAmount / us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis = us-gaap_NetInvestmentHedgingMember

X

- Definition

Asset Net Amount

+ References

No definition available.

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Period Type:	instant

X

- Definition

Cash Collateral Pledged

+ References

No definition available.

+ Details

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X

- Definition

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X

- Definition

Gross Amount of Financial and Derivative Assets Not Offset in the Statement of Financial Condition, Financial Instruments

+ References

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- Definition

Gross Amount of Liabilities Not Offset in the Statement of Financial Condition, Financial Instruments.

+ References

No definition available.

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- Definition

Gross and Net Amounts of Financial and Derivative Assets Presented in the Statement of Financial Condition

+ References

No definition available.

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- Definition

Gross and Net Amounts of Financial and Derivative Liabilities Presented in the Statement of Financial Condition

+ References

No definition available.

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X

- Definition

Liability Net Amount

+ References

No definition available.

+ Details

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Namespace Prefix:	bx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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