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Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands | Jun. 30, 2022 | Dec. 31, 2021
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | $ 1,271,032 |  | $ 1,157,004 |
Available-for-sale securities, at fair value |  | 1,879,904 | [1] | 2,113,893 |
Investments |  | 96,519 |  | 117,804 |
Cash equivalents measured at NAV |  | 3,189 |  | 3,004 |
Derivative contracts, Assets | [2] |  |  | 52,129 |
Total Assets |  | 3,352,892 |  | 3,443,834 |
Financial instruments sold, but not yet purchased, at fair value |  | 811,902 |  | 756,150 |
Derivative contracts, Liabilities | [3] | 102,247 |  | 52,147 |
Total, Liabilities |  | 914,149 |  | 808,297 |
U.S. Government Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 55,870 |  | 10,774 |
Financial instruments sold, but not yet purchased, at fair value |  | 478,722 |  | 377,023 |
U.S. Government Agency Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 201,613 |  | 143,793 |
Available-for-sale securities, at fair value |  | 2,272 | [1] | 1,808 |
Financial instruments sold, but not yet purchased, at fair value |  | 56,721 |  | 37,395 |
Asset-Backed Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 128,314 |  | 132,087 |
Available-for-sale securities, at fair value |  | 243,588 |  | 291,054 |
Investments |  | 24,949 |  |  |
Corporate Fixed Income Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 230,175 |  | 255,999 |
Available-for-sale securities, at fair value |  | 686,906 | [1] | 791,893 |
Financial instruments sold, but not yet purchased, at fair value |  | 124,305 |  | 153,852 |
Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 56,622 |  | 75,056 |
Investments |  |  |  | 21,308 |
Financial instruments sold, but not yet purchased, at fair value |  | 25,034 |  | 28,482 |
State And Municipal Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 136,879 |  | 162,335 |
Available-for-sale securities, at fair value |  | 2,355 | [1] | 2,399 |
Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 34,919 |  | 60,406 |
Investments in Funds and Partnerships Measured at NAV [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 22,686 |  | 23,058 |
Derivative contracts, Assets | [2] | 102,248 |  |  |
Agency Mortgage-Backed Securities [Member] | Agency Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 349,887 |  | 335,050 |
Available-for-sale securities, at fair value |  | 875,784 | [1] | 952,186 |
Financial instruments sold, but not yet purchased, at fair value |  | 122,369 |  | 156,628 |
Agency Mortgage-Backed Securities [Member] | Commercial [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale securities, at fair value |  | 68,512 | [1] | 73,985 |
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, at fair value |  | 487 | [1] | 568 |
Auction Rate Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 13,965 |  | 13,032 |
Sovereign Debt [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 1,271,032 |  |  |
Financial instruments sold, but not yet purchased, at fair value |  |  |  | 2,770 |
Other [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned | [4] | 111,672 |  | 41,910 |
Financial instruments sold, but not yet purchased, at fair value | [5] | 4,751 |  |  |
Level 1 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 109,401 |  | 84,450 |
Investments |  | 11,505 |  | 24,110 |
Total Assets |  | 120,906 |  | 108,560 |
Financial instruments sold, but not yet purchased, at fair value |  | 501,598 |  | 405,505 |
Derivative contracts, Liabilities | [3] | 0 |  |  |
Total, Liabilities |  | 501,598 |  | 405,505 |
Level 1 [Member] | U.S. Government Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 55,870 |  | 10,774 |
Financial instruments sold, but not yet purchased, at fair value |  | 478,722 |  | 377,023 |
Level 1 [Member] | Corporate Fixed Income Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 1,639 |  | 183 |
Financial instruments sold, but not yet purchased, at fair value |  | 63 |  |  |
Level 1 [Member] | Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 51,892 |  | 73,493 |
Investments |  | 11,410 |  | 13,893 |
Financial instruments sold, but not yet purchased, at fair value |  | 22,813 |  | 28,482 |
Level 1 [Member] | Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 95 |  | 10,217 |
Level 1 [Member] | Auction Rate Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  |  |  |  |
Level 1 [Member] | Other [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments sold, but not yet purchased, at fair value | [5] | 0 |  |  |
Level 2 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 1,015,220 |  | 980,766 |
Available-for-sale securities, at fair value |  | 1,879,904 |  | 2,113,893 |
Investments |  | 1,706 |  | 16,013 |
Derivative contracts, Assets | [2] | 102,248 |  | 52,129 |
Total Assets |  | 2,999,078 |  | 3,162,801 |
Financial instruments sold, but not yet purchased, at fair value |  | 307,182 |  | 350,645 |
Derivative contracts, Liabilities |  | 102,247 |  | 52,147 | [3]
Total, Liabilities |  | 409,429 |  | 402,792 |
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 |  | 201,613 |  | 143,793 |
Available-for-sale securities, at fair value |  | 2,272 |  | 1,808 |
Financial instruments sold, but not yet purchased, at fair value |  | 56,721 |  | 37,395 |
Level 2 [Member] | Asset-Backed Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 83,103 |  | 67,381 |
Available-for-sale securities, at fair value |  |  |  | 291,054 |
Level 2 [Member] | Corporate Fixed Income Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 228,536 |  | 255,816 |
Available-for-sale securities, at fair value |  | 686,906 |  | 791,893 |
Financial instruments sold, but not yet purchased, at fair value |  | 124,242 |  | 153,852 |
Level 2 [Member] | Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 3,717 |  | 1,338 |
Investments |  | 1,661 |  | 1,661 |
Financial instruments sold, but not yet purchased, at fair value |  | 2,221 |  |  |
Level 2 [Member] | State And Municipal Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 136,879 |  | 162,335 |
Available-for-sale securities, at fair value |  | 2,355 |  | 2,399 |
Level 2 [Member] | Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 45 |  | 14,352 |
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 |  | 349,887 |  | 335,050 |
Available-for-sale securities, at fair value |  | 875,784 |  | 952,186 |
Financial instruments sold, but not yet purchased, at fair value |  | 122,369 |  | 156,628 |
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, at fair value |  | 68,512 |  | 73,985 |
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, at fair value |  | 487 |  | 568 |
Level 2 [Member] | Auction Rate Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  |  |  |  |
Level 2 [Member] | Sovereign Debt [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments sold, but not yet purchased, at fair value |  |  |  | 2,770 |
Level 2 [Member] | Other [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 11,485 | [2] | 15,053 | [4]
Financial instruments sold, but not yet purchased, at fair value |  | 1,629 |  |  |
Level 3 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 146,411 |  | 91,788 |
Investments |  | 60,622 |  | 54,623 |
Derivative contracts, Assets | [2] | 0 |  |  |
Total Assets |  | 207,033 |  | 146,411 |
Financial instruments sold, but not yet purchased, at fair value |  | 3,122 |  |  |
Derivative contracts, Liabilities | [3] | 0 |  |  |
Total, Liabilities |  | 3,122 |  |  |
Level 3 [Member] | Asset-Backed Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 45,211 |  | 64,706 |
Level 3 [Member] | Corporate Equity Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned |  | 1,013 |  | 225 |
Investments |  | 11,878 |  | 5,754 |
Level 3 [Member] | Other Investment [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 34,779 |  | 35,837 |
Level 3 [Member] | Auction Rate Securities [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Investments |  | 13,965 |  | 13,032 |
Level 3 [Member] | Other [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Financial instruments owned | [4] | 100,187 |  | $ 26,857 |
Financial instruments sold, but not yet purchased, at fair value | [5] | $ 3,122 |  |  |
[1] | Due to the immaterial amount of income recognized on tax-exempt securities, yields were not calculated on a tax-equivalent basis.
[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] | Includes loans, non-agency mortgage-backed securities, and sovereign debt.
[5] | Includes loans, state and municipal securities, and sovereign debt.

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