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Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands | Mar. 31, 2023 | Dec. 31, 2022
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | $ 973,802 |  | $ 731,752 |
Available-for-sale securities |  | 1,624,458 |  | 1,636,041 |
Investments |  | 101,875 |  | 99,376 |
Cash equivalents measured at NAV |  | 2,569 |  | 1,650 |
Derivative Assets |  | 116,772 | [1] | 142,042 | [2]
Total Assets |  | 2,819,476 |  | 2,610,861 |
Financial instruments sold, but not yet purchased, at fair value |  | 653,881 |  | 454,817 |
Derivative contracts, Liabilities | [3] | 116,758 |  | 142,028 |
Total, Liabilities |  | 770,639 |  | 596,845 |
U.S. Government Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 42,530 |  | 38,956 |
Financial instruments sold, but not yet purchased, at fair value |  | 377,430 |  | 254,265 |
U.S. Government Agency Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 157,385 |  | 73,608 |
Available-for-sale securities |  | 2,189 | [4] | 2,148 |
Financial instruments sold, but not yet purchased, at fair value |  | 29,110 |  | 3,971 |
Asset-Backed Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 46,691 |  | 8,270 |
Available-for-sale securities |  | 209,540 | [4] | 207,725 |
Corporate Fixed Income Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 203,332 |  | 202,169 |
Available-for-sale securities |  | 550,322 | [4] | 566,294 |
Financial instruments sold, but not yet purchased, at fair value |  | 175,354 |  | 134,381 |
Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 46,995 |  | 38,129 |
Investments |  | 23,779 |  | 23,597 |
Financial instruments sold, but not yet purchased, at fair value |  | 15,148 |  | 11,590 |
State And Municipal Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 101,033 |  | 126,237 |
Available-for-sale securities |  | 2,351 | [4] | 2,351 |
Auction Rate Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 14,680 |  | 14,681 |
Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 37,513 | [5] | 37,136 | [6]
Investments in Funds and Partnerships Measured at NAV [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 25,903 |  | 23,962 |
Agency Mortgage-Backed Securities [Member] | Agency Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 276,964 |  | 172,642 |
Available-for-sale securities |  | 792,969 | [4] | 791,022 |
Financial instruments sold, but not yet purchased, at fair value |  | 50,768 |  | 44,793 |
Agency Mortgage-Backed Securities [Member] | Commercial [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities |  | 66,695 | [4] | 66,113 |
Agency Mortgage-Backed Securities [Member] | Non-Agency [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities |  | 392 | [4] | 388 |
Sovereign Debt [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 973,802 |  | 731,752 |
Other [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 98,872 | [7] | 71,741 | [8]
Financial instruments sold, but not yet purchased, at fair value |  | 6,071 | [9] | 5,817 | [10]
Level 1 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities |  | 0 |  |  |
Investments |  | 10,321 |  | 10,045 |
Derivative Assets | [1] | 0 |  |  |
Total Assets |  | 99,855 |  | 87,073 |
Financial instruments sold, but not yet purchased, at fair value |  | 392,771 |  | 265,943 |
Total, Liabilities |  | 392,771 |  | 265,943 |
Level 1 [Member] | U.S. Government Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 42,530 |  | 38,956 |
Financial instruments sold, but not yet purchased, at fair value |  | 377,430 |  | 254,265 |
Level 1 [Member] | Corporate Fixed Income Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 269 |  | 689 |
Financial instruments sold, but not yet purchased, at fair value |  | 193 |  | 88 |
Level 1 [Member] | Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 46,735 |  | 37,383 |
Investments |  | 10,221 |  | 9,928 |
Financial instruments sold, but not yet purchased, at fair value |  | 15,148 |  | 11,590 |
Level 1 [Member] | Auction Rate Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  |  |  | 0 |
Level 1 [Member] | Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 100 | [5] | 117 | [6]
Level 1 [Member] | Sovereign Debt [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 89,534 |  | 77,028 |
Level 2 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities |  | 1,624,458 |  | 1,636,041 |
Investments |  | 1,725 |  | 1,836 |
Derivative Assets |  | 116,772 | [1] | 142,042 | [2]
Total Assets |  | 2,531,508 |  | 2,362,576 |
Financial instruments sold, but not yet purchased, at fair value |  | 255,221 |  | 183,093 |
Derivative contracts, Liabilities |  | 116,758 | [3] | 142,028 | [11]
Total, Liabilities |  | 371,979 |  | 325,121 |
Level 2 [Member] | U.S. Government Agency Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 157,385 |  | 73,608 |
Available-for-sale securities |  | 2,189 |  | 2,148 |
Financial instruments sold, but not yet purchased, at fair value |  | 29,110 |  | 3,971 |
Level 2 [Member] | Asset-Backed Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 44,567 |  | 6,091 |
Available-for-sale securities |  | 209,540 |  | 207,725 |
Level 2 [Member] | Corporate Fixed Income Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 203,063 |  | 201,480 |
Available-for-sale securities |  | 550,322 |  | 566,294 |
Financial instruments sold, but not yet purchased, at fair value |  | 175,161 |  | 134,293 |
Level 2 [Member] | Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 260 |  | 746 |
Investments |  | 1,680 |  | 1,791 |
Level 2 [Member] | State And Municipal Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 101,033 |  | 126,237 |
Available-for-sale securities |  | 2,351 |  | 2,351 |
Level 2 [Member] | Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 45 | [5] | 0 |
Level 2 [Member] | Agency Mortgage-Backed Securities [Member] | Agency Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 276,964 |  | 172,642 |
Available-for-sale securities |  | 792,969 |  | 791,022 |
Financial instruments sold, but not yet purchased, at fair value |  | 50,768 |  | 44,793 |
Level 2 [Member] | Agency Mortgage-Backed Securities [Member] | Commercial [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities |  | 66,695 |  | 66,113 |
Level 2 [Member] | Agency Mortgage-Backed Securities [Member] | Non-Agency [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities |  | 392 |  | 388 |
Level 2 [Member] | Sovereign Debt [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 788,553 |  | 582,657 |
Level 2 [Member] | Other [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 5,281 | [7] | 1,853 | [8]
Investments | [6] |  |  | 45 |
Financial instruments sold, but not yet purchased, at fair value |  | 182 | [9] | 36 | [10]
Level 3 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities |  | 0 |  |  |
Investments |  | 63,926 |  | 63,533 |
Derivative Assets | [1] | 0 |  |  |
Total Assets |  | 159,641 |  | 135,600 |
Financial instruments sold, but not yet purchased, at fair value |  | 5,889 |  | 5,781 |
Total, Liabilities |  | 5,889 |  | 5,781 |
Level 3 [Member] | Asset-Backed Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 2,124 |  | 2,179 |
Level 3 [Member] | Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 11,878 |  | 11,878 |
Level 3 [Member] | Auction Rate Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 14,680 |  | 14,681 |
Level 3 [Member] | Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments | [5] | 37,368 |  |  |
Level 3 [Member] | Sovereign Debt [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 95,715 |  | 72,067 |
Level 3 [Member] | Other [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 93,591 | [7] | 69,888 | [8]
Investments | [6] |  |  | 36,974 |
Financial instruments sold, but not yet purchased, at fair value |  | $ 5,889 | [9] | $ 5,781 | [10]
[1] | Included in other assets in the consolidated statements of financial condition.
[2] | Included in other assets in the consolidated statements of financial condition.
[3] | Included in accounts payable and accrued expenses in the consolidated statements of financial condition.
[4] | Due to the immaterial amount of income recognized on tax-exempt securities, yields were not calculated on a tax-equivalent basis.
[5] | Primarily includes private company investments.
[6] | Primarily includes private company investments.
[7] | Includes syndicated loans, non-agency mortgage-backed securities, and sovereign debt.
[8] | Includes syndicated loans, non-agency mortgage-backed securities, and sovereign debt.
[9] | Includes syndicated loans and sovereign debt.
[10] | Includes syndicated loans and state and municipal securities
[11] | Included in accounts payable and accrued expenses in the consolidated statements of financial condition.

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