v2.4.1.9

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

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