Regulated Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Regulatory Matters [Line Items]
Consolidated entities net assets restricted as to payment of cash dividends and advances to partnership	$ 13.2

Consolidated entities' net assets restricted as to payment of cash dividends and advances to partnership.

No definition available.

Name:	bx_ConsolidatedEntitiesNetAssetsRestrictedAsToPaymentOfCashDividendsAndAdvancesToPartnership
Namespace Prefix:	bx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant