v2.4.1.9

Summary of Fair Value Transfers Between Level I and Level II (Detail) (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] |  |  |  |
Transfers from Level I into Level II | $ 0 bx_TransfersFromLevelOneToLevelTwo | [1] | $ 0 bx_TransfersFromLevelOneToLevelTwo | [1]
Transfers from Level II into Level I | $ 5,688 bx_TransfersFromLevelTwoToLevelOne | [2] | $ 18,029 bx_TransfersFromLevelTwoToLevelOne | [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
Name: | bx_TransfersFromLevelOneToLevelTwo
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
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration