Receivable From Brokers (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Receivables from Brokerage Clients [Line Items]
Receivable from brokers	$ 83,917	$ 85,401
Required collateral
Receivables from Brokerage Clients [Line Items]
Receivable from brokers	29,900	26,411
Cash In Excess Of Required Collateral
Receivables from Brokerage Clients [Line Items]
Receivable from brokers	52,437	58,791
Open spot foreign exchange positions
Receivables from Brokerage Clients [Line Items]
Receivable from brokers	$ 1,580	$ 199

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. Includes disclosure of claims held for amounts due a company. Examples include trade accounts receivables, notes receivables, loans receivables.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3, 4

-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 210.5-02.3)

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

Name:	us-gaap_ReceivablesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant