Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Sep. 30, 2024		Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 1,351,298		$ 918,741
Available-for-sale securities, Fair Value		1,618,289	[1]	1,551,686
Investments		93,050		91,105
Cash equivalents measured at NAV		1,768		4,706
Derivative contracts, Assets		95,327	[2]	118,668	[3]
Total Assets		3,159,732		2,684,906
Financial instruments sold, but not yet purchased, at fair value		768,909		497,741
Derivative contracts, Liabilities		95,314	[4]	118,651	[5]
Liabilities, Fair Value Disclosure, Total		864,223		616,392
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		19,662		32,411
Financial instruments sold, but not yet purchased, at fair value		441,703		273,653
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		198,038		106,634
Available-for-sale securities, Fair Value		2,298	[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		96,290		19,604
Available-for-sale securities, Fair Value		133,325		177,853
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		302,247		237,671
Available-for-sale securities, Fair Value		486,817	[1]	556,161
Financial instruments sold, but not yet purchased, at fair value		186,964		138,359
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		58,526		52,520
Investments		25,887		22,406
Financial instruments sold, but not yet purchased, at fair value		24,221		21,576
State and Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		244,491		223,155
Available-for-sale securities, Fair Value		2,351	[1]	2,351
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		738		783
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		39,382	[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		27,043		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		369,513		159,903
Available-for-sale securities, Fair Value		925,385	[1]	746,170
Financial instruments sold, but not yet purchased, at fair value		114,969		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		67,898	[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		215	[1]	261
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,351,298		918,741
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		62,531	[8]	86,843	[9]
Financial instruments sold, but not yet purchased, at fair value		1,052	[10]	6,565	[11]
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		13,830		10,386
Total Assets		90,097		95,165
Financial instruments sold, but not yet purchased, at fair value		465,924		295,229
Liabilities, Fair Value Disclosure, Total		465,924		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		19,662		32,411
Financial instruments sold, but not yet purchased, at fair value		441,703		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		56,605		52,158
Investments		13,795		10,313
Financial instruments sold, but not yet purchased, at fair value		24,221		21,576
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		35	[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		76,267		84,779
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value		1,618,289		1,551,686
Investments		214		330
Derivative contracts, Assets		95,327	[2]	118,668	[3]
Total Assets		2,929,201		2,420,184
Financial instruments sold, but not yet purchased, at fair value		302,267		198,676
Derivative contracts, Liabilities		95,314	[4]	118,651	[5]
Liabilities, Fair Value Disclosure, Total		397,581		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		198,038		106,634
Available-for-sale securities, Fair Value		2,298		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		95,155		18,106
Available-for-sale securities, Fair Value		133,325		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		302,247		237,461
Available-for-sale securities, Fair Value		486,817		556,161
Financial instruments sold, but not yet purchased, at fair value		186,964		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		1,921		362
Investments		214		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		244,491		223,155
Available-for-sale securities, Fair Value		2,351		2,351
Level 2 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[7]			115
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		369,513		159,903
Available-for-sale securities, Fair Value		925,385		746,170
Financial instruments sold, but not yet purchased, at fair value		114,969		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		67,898		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		215		261
Level 2 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,215,371		749,500
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		4,006	[8]	3,879	[9]
Financial instruments sold, but not yet purchased, at fair value		334	[10]	2,729	[11]
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		51,963		52,128
Total Assets		111,623		136,590
Financial instruments sold, but not yet purchased, at fair value		718		3,836
Liabilities, Fair Value Disclosure, Total		718		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		1,135		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		738		783
Level 3 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		39,347	[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		59,660		84,462
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		58,525	[8]	82,964	[9]
Financial instruments sold, but not yet purchased, at fair value		$ 718	[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, U.S. government agency securities, and sovereign debt.

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