v2.4.1.9
Summary of Changes in Financial Assets Measured at Fair Value for Which Level III Inputs Were Used (Detail) (Level 3, USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Balance, Beginning of Period $ 3,740,693us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue $ 3,555,138us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Transfer In Due to Consolidation and Acquisition   276,806bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferringDueToConsolidationAndAcquisition [1]
Transfer In (Out) Due to Deconsolidation   (83,867)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutDueToDeconsolidation
Transfer In to Level III 156,778bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferInToLevelIii [2] 199,286bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferInToLevelIii [2]
Transfer Out of Level III (225,085)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutOfLevelIii [2] (245,317)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutOfLevelIii [2]
Purchases 319,341us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases 318,491us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Sales (186,604)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales (451,568)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Settlements (1,247)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements (1,325)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Changes in Gains (Losses) Included in Earnings and Other Comprehensive Income (23)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsAndOtherComprehensiveIncomeLoss 17,117bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsAndOtherComprehensiveIncomeLoss
Balance, End of Period 3,803,853us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue 3,584,761us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Changes in Unrealized (Gains) Losses Included in Earnings Related to Liabilities Still Held at the Reporting Date 30,599us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss 26,545us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
Investments Of Consolidated Funds
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Balance, Beginning of Period 3,498,033us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 3,358,752us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Transfer In Due to Consolidation and Acquisition   276,806bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferringDueToConsolidationAndAcquisition
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [1]
Transfer In (Out) Due to Deconsolidation   (83,867)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutDueToDeconsolidation
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Transfer In to Level III 129,848bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferInToLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2] 195,607bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferInToLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2]
Transfer Out of Level III (202,401)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutOfLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2] (244,308)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutOfLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2]
Purchases 288,222us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 159,613us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Sales (147,181)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 (290,782)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Changes in Gains (Losses) Included in Earnings and Other Comprehensive Income 10,054bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsAndOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 17,015bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsAndOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Balance, End of Period 3,576,575us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 3,388,836us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Changes in Unrealized (Gains) Losses Included in Earnings Related to Liabilities Still Held at the Reporting Date 29,891us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 23,986us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentsOfConsolidatedFundsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Loans And Receivables
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Balance, Beginning of Period 40,397us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 137,788us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Purchases 6,186us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 81,241us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Sales (4,071)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 (156,719)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Settlements (1,144)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 (1,170)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Changes in Gains (Losses) Included in Earnings and Other Comprehensive Income (677)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsAndOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		  
Balance, End of Period 40,691us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 61,140us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Changes in Unrealized (Gains) Losses Included in Earnings Related to Liabilities Still Held at the Reporting Date (806)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 433us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_LoansAndReceivablesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Other
    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Balance, Beginning of Period 202,263us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3] 58,598us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3]
Transfer In to Level III 26,930bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferInToLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2],[3] 3,679bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferInToLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2],[3]
Transfer Out of Level III (22,684)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutOfLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2],[3] (1,009)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransferOutOfLevelIii
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [2],[3]
Purchases 24,933us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3] 77,637us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3]
Sales (35,352)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3] (4,067)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3]
Settlements (103)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3] (155)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3]
Changes in Gains (Losses) Included in Earnings and Other Comprehensive Income (9,400)bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsAndOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3] 102bx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsAndOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3]
Balance, End of Period 186,587us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3] 134,785us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3]
Changes in Unrealized (Gains) Losses Included in Earnings Related to Liabilities Still Held at the Reporting Date $ 1,514us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3] $ 2,126us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= bx_InvestmentAssetOtherMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [3]
[1] Represents the transfer into Level III of financial assets and liabilities as a result of the consolidation of certain fund entities, the acquisition of management contracts and the Harbourmaster acquisition.
[2] Transfers in and out of Level III financial assets and liabilities were due to changes in the observability of inputs used in the valuation of such assets and liabilities.
[3] Represents Blackstone's Treasury Cash Management Strategies and Other Investments.