This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets) in trading revenues; the fair value of which assets was or is measured on a recurring basis using significant unobservable inputs (Level 3).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Commitments and Contingent liabilities - Fair Value of Asset or Liability on Futures Contracts Activity (Detail) (Futures Contracts [Member], USD $) In Thousands, unless otherwise specified					3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Payable to Broker Dealer [Member]	Dec. 31, 2012 Payable to Broker Dealer [Member]	Jun. 30, 2013 Net trading revenue [Member]	Jun. 30, 2012 Net trading revenue [Member]	Jun. 30, 2013 Net trading revenue [Member]	Jun. 30, 2012 Net trading revenue [Member]
Sale Leaseback Transaction [Line Items]
Notional Value	$ (205,761)	$ (180,512)
Fair Value			(836)	(1,923)
Unrealized gain					$ 4,181	$ 16,266	$ 6,449	$ 11,426