v2.4.1.9

Senior Secured Notes and Subordinated Notes (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Senior Secured Notes
Debt Instrument [Line Items]
Fair Value	$ 6,587,954us-gaap_NotesPayableFairValueDisclosure / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember	$ 6,448,352us-gaap_NotesPayableFairValueDisclosure / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
Subordinated Notes
Debt Instrument [Line Items]
Fair Value	345,793us-gaap_NotesPayableFairValueDisclosure / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember	348,752us-gaap_NotesPayableFairValueDisclosure / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember
Non-Consolidated Affiliates Senior Secured Notes | Senior Secured Notes
Debt Instrument [Line Items]
Borrowing Outstanding		2,500us-gaap_DebtInstrumentCarryingAmount / dei_LegalEntityAxis = bx_NonConsolidatedAffiliatesSeniorSecuredNotesMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
Fair Value		2,504us-gaap_NotesPayableFairValueDisclosure / dei_LegalEntityAxis = bx_NonConsolidatedAffiliatesSeniorSecuredNotesMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
Non-Consolidated Affiliates Senior Secured Notes | Subordinated Notes
Debt Instrument [Line Items]
Borrowing Outstanding	34,200us-gaap_DebtInstrumentCarryingAmount / dei_LegalEntityAxis = bx_NonConsolidatedAffiliatesSeniorSecuredNotesMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember	24,200us-gaap_DebtInstrumentCarryingAmount / dei_LegalEntityAxis = bx_NonConsolidatedAffiliatesSeniorSecuredNotesMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember
Fair Value	$ 23,543us-gaap_NotesPayableFairValueDisclosure / dei_LegalEntityAxis = bx_NonConsolidatedAffiliatesSeniorSecuredNotesMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember	$ 14,377us-gaap_NotesPayableFairValueDisclosure / dei_LegalEntityAxis = bx_NonConsolidatedAffiliatesSeniorSecuredNotesMember / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorSubordinatedNotesMember

X

- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20

-Article 5



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Fair value portion of notes payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19,20,22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_NotesPayableFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	dei_LegalEntityAxis=bx_NonConsolidatedAffiliatesSeniorSecuredNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorSubordinatedNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: