Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Mar. 31, 2024		Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 1,230,855		$ 918,741
Available-for-sale securities, Fair Value		1,499,982	[1]	1,551,686
Investments		89,518		91,105
Cash equivalents measured at NAV		2,013		4,706
Derivative contracts, Assets		127,701	[2]	118,668	[3]
Total Assets		2,950,069		2,684,906
Financial instruments sold, but not yet purchased, at fair value		682,279		497,741
Derivative contracts, Liabilities		127,680	[4]	118,651	[5]
Total, Liabilities		809,959		616,392
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		19,071		32,411
Financial instruments sold, but not yet purchased, at fair value		411,916		273,653
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		195,116		106,634
Available-for-sale securities, Fair Value		2,209	[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		80,121		19,604
Available-for-sale securities, Fair Value		171,385		177,853
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		340,239		237,671
Available-for-sale securities, Fair Value		542,997	[1]	556,161
Financial instruments sold, but not yet purchased, at fair value		164,227		138,359
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		62,434		52,520
Investments		22,874		22,406
Financial instruments sold, but not yet purchased, at fair value		45,530		21,576
State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		224,714		223,155
Available-for-sale securities, Fair Value		2,350	[1]	2,351
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		783		783
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[6]			39,655
Investments in Funds and Partnerships Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		26,265		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		208,299		159,903
Available-for-sale securities, Fair Value		713,939	[1]	746,170
Financial instruments sold, but not yet purchased, at fair value		56,755		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		66,854	[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		248	[1]	261
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,230,855		918,741
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		100,861	[7]	86,843	[8]
Investments	[9]	39,596
Financial instruments sold, but not yet purchased, at fair value		3,851	[10]	6,565	[11]
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		10,813		10,386
Total Assets		92,008		95,165
Financial instruments sold, but not yet purchased, at fair value		457,491		295,229
Total, Liabilities		457,491		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		19,071		32,411
Financial instruments sold, but not yet purchased, at fair value		411,916		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		48		210
Financial instruments sold, but not yet purchased, at fair value		45
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		62,076		52,158
Investments		10,780		10,313
Financial instruments sold, but not yet purchased, at fair value		45,530		21,576
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[6]			73
Level 1 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		81,195		84,779
Level 1 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[9]	33
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value		1,499,982		1,551,686
Investments		312		330
Derivative contracts, Assets		127,701	[2]	118,668	[3]
Total Assets		2,678,686		2,420,184
Financial instruments sold, but not yet purchased, at fair value		221,039		198,676
Derivative contracts, Liabilities		127,680	[4]	118,651	[5]
Total, Liabilities		348,719		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		195,116		106,634
Available-for-sale securities, Fair Value		2,209		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		78,882		18,106
Available-for-sale securities, Fair Value		171,385		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		340,191		237,461
Available-for-sale securities, Fair Value		542,997		556,161
Financial instruments sold, but not yet purchased, at fair value		164,182		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		358		362
Investments		216		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		224,714		223,155
Available-for-sale securities, Fair Value		2,350		2,351
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		208,299		159,903
Available-for-sale securities, Fair Value		713,939		746,170
Financial instruments sold, but not yet purchased, at fair value		56,755		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		66,854		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		248		261
Level 2 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,050,691		749,500
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		3,131	[7]	3,879	[8]
Investments		96	[9]	115	[6]
Financial instruments sold, but not yet purchased, at fair value		102	[10]	2,729	[11]
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		52,128		52,128
Total Assets		151,097		136,590
Financial instruments sold, but not yet purchased, at fair value		3,749		3,836
Total, Liabilities		3,749		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		1,239		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		783		783
Level 3 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		98,969		84,462
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		97,730	[7]	82,964	[8]
Investments		39,467	[9]	39,467	[6]
Financial instruments sold, but not yet purchased, at fair value		$ 3,749	[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] Includes syndicated loans, non-agency mortgage-backed securities, and sovereign debt.

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

[9] Primarily includes private company investments.

[10] Includes syndicated loans, U.S. government agency securities, and state and municipal securities.

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