Revenues from Contracts with Customers (Revenues from Contracts with Customers Disaggregated by Major Business Activity and Primary Geographic Regions) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Commissions	$ 165,775	$ 175,274
Investment banking	176,362	126,852
Asset management and service fees	195,801	$ 162,739
Other	3,718
Total	541,656
Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	78,689
Advisory Fees [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	97,673
Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Commissions	119,205
Asset management and service fees	195,789
Other	3,718
Total	326,400
Global Wealth Management [Member] \| Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	7,688
Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Commissions	46,570
Asset management and service fees	12
Total	215,256
Institutional Group [Member] \| Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	71,001
Institutional Group [Member] \| Advisory Fees [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	97,673
United States [Member]
Disaggregation Of Revenue [Line Items]
Total	502,750
United States [Member] \| Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Total	326,400
United States [Member] \| Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Total	176,350
Europe [Member]
Disaggregation Of Revenue [Line Items]
Total	37,879
Europe [Member] \| Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Total	37,879
Other [Member]
Disaggregation Of Revenue [Line Items]
Total	1,027
Other [Member] \| Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Total	$ 1,027

Other revenue from contracts with customer.

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- Definition

Amount of commission revenue from buying and selling securities on behalf of customers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 05
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=68070981&loc=d3e40544-110947

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(a),(b))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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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.

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- Definition

Amount of revenue from providing investment advisory, asset management and administrative services, including, but not limited to, distribution and shareholder services, accounting, tax, legal, regulatory filing, share registration, and shareholder correspondence activities.

+ References

No definition available.

+ Details

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- Definition

Includes (1) underwriting revenue (the spread between the resale price received and the cost of the securities and related expenses) generated through the purchasing, distributing and reselling of new issues of securities (alternatively, could be a secondary offering of a large block of previously issued securities); and (2) fees earned for mergers, acquisitions, divestitures, restructurings, and other types of financial advisory services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(b),(d))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045

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