v2.4.0.8

Information for Financial Instruments on Which Fair Value Option was Elected (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
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Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Uncollected principal balance on financial instruments that exceeded fair value total | $ (353,954) |  | $ (587,726) |
Fair value of financial instruments more than one day past due | 52,986 | [1] | 36,153 | [1]
Uncollected principal balance on financial instruments that exceeds fair value more than one day past due | (143,727) | [1] | (73,335) | [1]
Loans And Receivables |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Uncollected principal balance on financial instruments that exceeded fair value total | (1,223) |  | (292) |
Corporate Loans |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Uncollected principal balance on financial instruments that exceeded fair value total | (351,515) |  | (586,450) |
Fair value of financial instruments more than one day past due | 52,986 | [1] | 35,322 | [1]
Uncollected principal balance on financial instruments that exceeds fair value more than one day past due | (143,727) | [1] | (73,291) | [1]
Corporate Bonds |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Uncollected principal balance on financial instruments that exceeded fair value total | (1,216) |  | (984) |
Fair value of financial instruments more than one day past due |  |  | 831 | [1]
Uncollected principal balance on financial instruments that exceeds fair value more than one day past due |  |  | $ (44) | [1]
[1] | Past due Corporate Loans and Corporate Bonds within CLO assets are classified as past due if contractual payments are more than one day past due.

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- Definition Fair Value of Financial Instruments More Than One Day Past Due + References No definition available. + Details
Name: | bx_FairValueOfFinancialInstrumentsMoreThanOneDayPastDue
Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Uncollected Principal Balance on Financial Instruments That Exceeded Fair Value Total + References No definition available. + Details
Name: | bx_UncollectedPrincipalBalanceOnFinancialInstrumentsThatExceededFairValueTotal
Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Uncollected Principal Balance On Financial Instruments That Exceeded Fair Value More than One Day Past Due + References No definition available. + Details
Name: | bx_UncollectedPrincipalBalanceOnFinancialInstrumentsThatExceedsFairValueMoreThanOneDayPastDue
Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_FairValueOptionQuantitativeDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration