v2.4.1.9
Fair Value Option - Additional Information (Detail) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair value of financial instruments more than one day past due $ 2,875,000bx_FairValueOfFinancialInstrumentsMoreThanOneDayPastDue [1] $ 4,369,000bx_FairValueOfFinancialInstrumentsMoreThanOneDayPastDue [1]
Corporate Bonds    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair value of financial instruments more than one day past due 0bx_FairValueOfFinancialInstrumentsMoreThanOneDayPastDue
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateBondSecuritiesMember		 0bx_FairValueOfFinancialInstrumentsMoreThanOneDayPastDue
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateBondSecuritiesMember
Fair value of financial instruments with non-accrual status 0bx_InvestmentSecuritiesFairValueDisclosureOnNonaccrualStatus
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateBondSecuritiesMember		 0bx_InvestmentSecuritiesFairValueDisclosureOnNonaccrualStatus
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateBondSecuritiesMember
Loans And Receivables    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair value of financial instruments more than one day past due   0bx_FairValueOfFinancialInstrumentsMoreThanOneDayPastDue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= bx_LoansAndReceivablesMember
Fair value of financial instruments with non-accrual status   $ 0bx_InvestmentSecuritiesFairValueDisclosureOnNonaccrualStatus
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= bx_LoansAndReceivablesMember
[1] Corporate Loans and Corporate Bonds within CLO assets are classified as past due if contractual payments are more than one day past due.