Revenues from Contracts with Customers (Schedule of Total Revenues Broken Out by Revenues from Contracts with Customers and Other Sources of Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Revenues
Revenue from contracts with customers	$ 516,338	$ 541,656
Other	3,782	3,718
Total revenue from contracts with customers	516,338	541,656
Other sources of revenue:
Interest	191,071	137,734
Principal transactions	104,032	97,782
Other	8,427	(361)
Total revenues	819,868	776,811
Commissions [Member]
Revenues
Revenue from contracts with customers	155,449	165,775
Investment Banking [Member]
Revenues
Revenue from contracts with customers	161,840	176,362
Asset Management and Service Fees [Member]
Revenues
Revenue from contracts with customers	$ 195,267	$ 195,801

Other revenue from contracts with customer.

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Other revenues.

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Other sources of revenue.

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Revenue from contract with customer excluding other segment revenue and assessed tax.

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Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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Amount of realized and unrealized gain (loss) resulting from the difference between acquisition price and selling price or fair value of trading assets and trading liabilities, and from the firm's direct investment activity, conducted separately from customer trading activities, including, but not limited to, investments in private equity, alternative investment products, real estate, and exchanges and memberships.

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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.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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