Receivables From And Payables To Brokers, Dealers, And Clearing Agencies (Schedule Of Due To (From) Broker-Dealers And Clearing Organizations) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Receivables from Brokers-Dealers and Clearing Agencies [Abstract]
Deposits with clearing agencies	$ 750	$ 750
Unsettled regular way trades, net	14,520	3,337
Receivables from clearing agencies	93,600	77,091
Receivables from brokers, dealers, and clearing agencies	108,870	81,178
Payables to Broker-Dealers and Clearing Agencies [Abstract]
Margin payable	32,602	85,761
Payables to brokers, dealers, and clearing agencies	$ 32,602	$ 85,761

Receivables from unsettled regular way trades, net.

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- Definition

Amount of right to receive cash and securities on deposit with broker-dealers to demonstrate an intention to complete a purchase (good faith deposit) and collateral deposited by counterparty to cover the credit risk assumed (margin deposit).

+ References

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- Definition

Amount of other payables due to broker-dealers or clearing organizations.

+ References

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Amount payable to broker-dealers and clearing organizations, including, but not limited to, securities failed-to-receive, certain deposits received for securities loaned, open transactions, and floor-brokerage payables.

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Amount receivable from broker-dealers and clearing organizations, including, but not limited to, securities failed-to-deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=35710130&loc=d3e41645-110958

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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Amount of right to receive cash and securities on deposit with clearing organizations. Clearing organizations perform post trade processing and trade comparisons among numerous broker-dealers and act as settlement agents between buying and selling broker-dealers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=35710059&loc=d3e41304-110954

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5066-111524

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