Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Dec. 31, 2023		Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 918,741		$ 731,752
Available-for-sale securities		1,551,686	[1]	1,636,041
Investments		91,105		99,376
Cash equivalents measured at NAV		4,706		1,650
Derivative contracts, Assets		118,668	[2]	142,042	[3]
Total Assets		2,684,906		2,610,861
Financial instruments sold, but not yet purchased, at fair value		497,741		454,817
Derivative contracts, Liabilities		118,651	[4]	142,028	[5]
Total Liabilities		616,392		596,845
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		32,411		38,956
Financial instruments sold, but not yet purchased, at fair value		273,653		254,265
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		106,634		73,608
Available-for-sale securities		2,219	[1]	2,148
Financial instruments sold, but not yet purchased, at fair value		4,924		3,971
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		19,604		8,270
Available-for-sale securities		177,853		207,725
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		237,671		202,169
Available-for-sale securities		556,161	[1]	566,294
Financial instruments sold, but not yet purchased, at fair value		138,359		134,381
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		52,520		38,129
Investments		22,406		23,597
Financial instruments sold, but not yet purchased, at fair value		21,576		11,590
State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		223,155		126,237
Available-for-sale securities		2,351	[1]	2,351
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		39,655	[6]	37,136	[7]
Investments In Funds And Partnerships Measured At Net Asset Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		28,261		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				172,642
Available-for-sale securities		746,170	[1]	791,022
Financial instruments sold, but not yet purchased, at fair value		52,664		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		66,671	[1]	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		261	[1]	388
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		783		14,681
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		918,741		731,752
Financial instruments sold, but not yet purchased, at fair value	[8]	6,565
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		86,843	[9]	71,741	[10]
Financial instruments sold, but not yet purchased, at fair value	[11]			5,817
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		10,386		10,045
Total Assets		95,165		87,073
Financial instruments sold, but not yet purchased, at fair value		295,229		265,943
Total Liabilities		295,229		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		32,411		38,956
Financial instruments sold, but not yet purchased, at fair value		273,653		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		210		689
Financial instruments sold, but not yet purchased, at fair value				88
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		52,158		37,383
Investments		10,313		9,928
Financial instruments sold, but not yet purchased, at fair value		21,576		11,590
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		73	[6]	117	[7]
Level 1 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		84,779		77,028
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		1,551,686		1,636,041
Investments		330		1,836
Derivative contracts, Assets		118,668	[2]	142,042	[3]
Total Assets		2,420,184		2,362,576
Financial instruments sold, but not yet purchased, at fair value		198,676		183,093
Derivative contracts, Liabilities		118,651	[4]	142,028	[5]
Total Liabilities		317,327		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		106,634		73,608
Available-for-sale securities		2,219		2,148
Financial instruments sold, but not yet purchased, at fair value		4,924		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		18,106		6,091
Available-for-sale securities		177,853		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		237,461		201,480
Available-for-sale securities		556,161		566,294
Financial instruments sold, but not yet purchased, at fair value		138,359		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		362		746
Investments		215		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		223,155		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		115	[6]	45	[7]
Level 2 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		159,903
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				172,642
Available-for-sale securities		746,170		791,022
Financial instruments sold, but not yet purchased, at fair value		52,664		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		66,671		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		261		388
Level 2 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		749,500		582,657
Financial instruments sold, but not yet purchased, at fair value	[8]	2,729
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		3,879	[9]	1,853	[10]
Financial instruments sold, but not yet purchased, at fair value				36
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		52,128		63,533
Total Assets		136,590		135,600
Financial instruments sold, but not yet purchased, at fair value		3,836		5,781
Total Liabilities		3,836		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		1,498		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] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		39,467	[6]	36,974	[7]
Level 3 [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		783		14,681
Level 3 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		84,462		72,067
Financial instruments sold, but not yet purchased, at fair value	[8]	3,836
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 82,964	[9]	69,888	[10]
Financial instruments sold, but not yet purchased, at fair value				$ 5,781

[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, state and municipal securities, and asset-backed securities.

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

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

[11] Includes syndicated loans and state and municipal securities.