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Securities Owned and Securities Sold, but not yet Purchased (and Fair Value Measurement) - Schedule of Securities Owned/Sold But Not Yet Purchased (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Securities Owned Total | $ 66,294 | $ 58,907
Securities Sold, but not yet Purchased Total | 950 | 1,248
Trading Securities [Member] |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Securities Owned Total | 1,691 | 1,556
Securities Sold, but not yet Purchased Total | 950 | 1,248
Available-for-sale Securities [Member] |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Securities Owned Total | $ 64,603 | $ 57,351

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Fair value of financial instruments held by a broker-dealer for their own account (proprietary securities) for trading or investment purposes determined by management based upon quoted prices of a financial instrument with similar characteristics or on a valuation technique or model. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
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- Definition Fair value of financial instruments sold short by a broker-dealer for their own account (proprietary securities) for trading or investment purposes determined by management based upon quoted prices of a financial instrument with similar characteristics or on a valuation technique or model. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
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