Receivable from and Payable to Brokers, Dealers, and Clearing Organizations - Schedule of Amounts Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Receivable/Payable:
Clearing organizations and other, Receivable	$ 1,096,308	$ 140,089
Securities failed to deliver, Receivable	233,805	2,880
Total Receivable	1,330,113	142,969
Clearing organizations and other, Payable	564,592	15,879
Securities failed to receive, Payable	101,586	8,306
Total Payable	$ 666,178	$ 24,185

Receivable from and Payable to Brokers, Dealers, and Clearing Organizations - Schedule of Amounts Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Detail) (USD $)
In Thousands, unless otherwise specified

Sep. 30, 2013

Dec. 31, 2012

Clearing organizations and other, Receivable

$ 1,096,308

$ 140,089

Securities failed to deliver, Receivable

233,805

2,880

Total Receivable

1,330,113

142,969

Clearing organizations and other, Payable

564,592

15,879

Securities failed to receive, Payable

101,586

8,306

Total Payable

$ 666,178

$ 24,185

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- Definition

Other amounts due but not specifically defined in the taxonomy to other broker-dealers or clearing organizations.

+ References

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- Definition

Amounts due that are not specifically identified in the taxonomy and are due from other broker-dealers.

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- Definition

Aggregate amounts payable to broker-dealers and clearing organizations include amounts payable for securities failed to receive, certain deposits received for securities loaned, amounts payable to clearing organizations on open transactions, and floor-brokerage payables. In addition, the net receivable or payable arising from unsettled trades would be reflected in those captions. A broker-dealer that purchases securities, either for its own account or for a customer's account, but does not receive the securities on the settlement date records the amount of money representing the purchase price of the securities, including any accrued interest, as a liability to the selling broker-dealer. This liability is paid when the securities are received by the purchasing broker-dealer.

+ References

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 80

-Subparagraph Exhibit 4-8, 4

-IssueDate 2006-05-01

-Chapter 4

-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.

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 24, 25

-IssueDate 2006-05-01

-Chapter 7

-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.

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 24-31, 35

-IssueDate 2006-05-01

-Chapter 4

-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.

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Amount receivable from securities failed to deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage items. Also cash and securities [guarantee] on deposit with [commodities] clearing organizations and other entities which provide services necessary to operations of the Company. This item would include, for instance, cash and securities advanced as [refundable] collateral for securities borrowed.

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Amount recorded when a Broker Dealer sells securities but does not deliver the securities on settlement date. The amount recorded is the selling price including any accrued interest. This asset is collected upon delivery of the securities.

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A broker-dealer that purchases securities but does not receive the securities by the agreed settlement date records the price of the securities and any accrued interest as a liability called Securities Failed-to-Receive to the selling broker. The liability is paid when the securities are received by the purchasing broker dealer.

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