v3.3.0.814

Summary of Fair Value Transfers Between Level I and Level II (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2015 | Sep. 30, 2015 | Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Transfers from Level I into Level II | [1] | $ 287 | $ 287 |
Transfers from Level II into Level I | [2] | $ 26,534 | $ 32,312 | $ 67,327
[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
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Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration