v2.4.0.8

Other Assets and Accounts Payable, Accrued Expenses and Other Liabilities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Schedule of Other Assets [Line Items] |  |  |
Depreciation expense | $ 33.6 | $ 34.0 | $ 31.6
Accounts Payable, Accrued Expenses and Other Liabilities for redemption to investors | 57.0 | 170.4 |
Payables relating to unsettled purchases | $ 229.1 | $ 352.3 |

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- Definition Accounts payable, accrued liabilities and other liabilities for redemption to investors. + References No definition available. + Details
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Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Accounts Payable for Unsettled Purchases + References No definition available. + Details
Name: | bx_AccountsPayableForUnsettledPurchases
Namespace Prefix: | bx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | bx_ScheduleOfOtherAssetsLineItems
Namespace Prefix: | bx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration