Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2024		Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	$ 1,261,216		$ 918,741
Available-for-sale securities, Fair Value	1,583,477	[1]	1,551,686
Investments	91,465		91,105
Cash equivalents measured at NAV	1,674		4,706
Derivative contracts, Assets	127,177	[2]	118,668	[3]
Total Assets	3,065,009		2,684,906
Financial instruments sold, but not yet purchased, at fair value	634,311		497,741
Derivative contracts, Liabilities	127,156	[4]	118,651	[5]
Liabilities, Fair Value Disclosure, Total	761,467		616,392
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	10,901		32,411
Financial instruments sold, but not yet purchased, at fair value	392,431		273,653
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	194,979		106,634
Available-for-sale securities, Fair Value	2,215	[1]	2,219
Financial instruments sold, but not yet purchased, at fair value			4,924
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	89,007		19,604
Available-for-sale securities, Fair Value	159,028		177,853
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	293,994		237,671
Available-for-sale securities, Fair Value	507,383	[1]	556,161
Financial instruments sold, but not yet purchased, at fair value	133,943		138,359
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	69,216		52,520
Investments	24,464		22,406
Financial instruments sold, but not yet purchased, at fair value	29,122		21,576
State and Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	271,417		223,155
Available-for-sale securities, Fair Value	2,337	[1]	2,351
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	739		783
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	39,387	[6]	39,655	[7]
Investments in Funds and Partnerships Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	26,875		28,261
Agency Mortgage-Backed Securities [Member] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	259,206		159,903
Available-for-sale securities, Fair Value	845,462	[1]	746,170
Financial instruments sold, but not yet purchased, at fair value	74,742		52,664
Agency Mortgage-Backed Securities [Member] | Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value	66,830	[1]	66,671
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, Fair Value	222	[1]	261
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,261,216		918,741
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	72,496	[8]	86,843	[9]
Financial instruments sold, but not yet purchased, at fair value	4,073	[10]	6,565	[11]
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	12,403		10,386
Total Assets	92,143		95,165
Financial instruments sold, but not yet purchased, at fair value	421,553		295,229
Liabilities, Fair Value Disclosure, Total	421,553		295,229
Level 1 [Member] | U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	10,901		32,411
Financial instruments sold, but not yet purchased, at fair value	392,431		273,653
Level 1 [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned			210
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	68,839		52,158
Investments	12,371		10,313
Financial instruments sold, but not yet purchased, at fair value	29,122		21,576
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	32	[6]	73	[7]
Level 1 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	79,740		84,779
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value	1,583,477		1,551,686
Investments	221		330
Derivative contracts, Assets	127,177	[2]	118,668	[3]
Total Assets	2,825,435		2,420,184
Financial instruments sold, but not yet purchased, at fair value	209,035		198,676
Derivative contracts, Liabilities	127,156	[4]	118,651	[5]
Liabilities, Fair Value Disclosure, Total	336,191		317,327
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	194,979		106,634
Available-for-sale securities, Fair Value	2,215		2,219
Financial instruments sold, but not yet purchased, at fair value			4,924
Level 2 [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	87,804		18,106
Available-for-sale securities, Fair Value	159,028		177,853
Level 2 [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	293,994		237,461
Available-for-sale securities, Fair Value	507,383		556,161
Financial instruments sold, but not yet purchased, at fair value	133,943		138,359
Level 2 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	377		362
Investments	215		215
Level 2 [Member] | State and Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	271,417		223,155
Available-for-sale securities, Fair Value	2,337		2,351
Level 2 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	6	[6]	115	[7]
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	259,206		159,903
Available-for-sale securities, Fair Value	845,462		746,170
Financial instruments sold, but not yet purchased, at fair value	74,742		52,664
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, Fair Value	66,830		66,671
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, Fair Value	222		261
Level 2 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,114,560		749,500
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	6,783	[8]	3,879	[9]
Financial instruments sold, but not yet purchased, at fair value	350	[10]	2,729	[11]
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	51,966		52,128
Total Assets	118,882		136,590
Financial instruments sold, but not yet purchased, at fair value	3,723		3,836
Liabilities, Fair Value Disclosure, Total	3,723		3,836
Level 3 [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,203		1,498
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	739		783
Level 3 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	39,349	[6]	39,467	[7]
Level 3 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	66,916		84,462
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	65,713	[8]	82,964	[9]
Financial instruments sold, but not yet purchased, at fair value	$ 3,723	[10]	$ 3,836	[11]

[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 other assets in the consolidated statements of financial condition.

[4] Included in accounts payable and accrued expenses in the consolidated statements of financial condition.

[5] Included in accounts payable and accrued expenses in the consolidated statements of financial condition

[6] Primarily includes private company investments.

[7] Primarily includes private company investments.

[8] Includes syndicated loans, non-agency mortgage-backed securities, and sovereign debt.

[9] Includes syndicated loans, non-agency mortgage-backed securities, and sovereign debt.

[10] Includes syndicated loans and sovereign debt.

[11] Includes syndicated loans, state and municipal securities, and asset-backed securities.