v2.4.0.8

Summary of Fair Value Transfers Between Level I and Level II (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2013 | Sep. 30, 2012 | Sep. 30, 2013 | Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Transfers from Level I into Level II |  |  | $ 288 | [1] | $ 31 | [1] | $ 45,440 | [1]
Transfers from Level II into Level I | $ 41,155 | [2] | $ 45 | [2] | $ 1,308 | [2] | $ 846 | [2]
[1] | Transfers out of Level I represent those financial instruments for which restrictions exist and adjustments were made to an otherwise observable price to reflect fair value at the reporting date.
[2] | Transfers into Level I represent those financial instruments for which an unadjusted quoted price in an active market became available for the identical asset.

X
- Definition Transfers from Level I into Level II + References No definition available. + Details
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Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Transfers from Level II into Level I + References No definition available. + Details
Name: | bx_TransfersFromLevelTwoToLevelOne
Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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