Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Sep. 30, 2023		Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 1,056,745		$ 731,752
Available-for-sale securities, at fair value		1,512,233	[1]	1,636,041
Investments		91,154		99,376
Cash equivalents measured at NAV		1,870		1,650
Derivative contracts, Assets	[2]	166,038		142,042
Total Assets		2,828,040		2,610,861
Financial instruments sold, but not yet purchased, at fair value		578,290		454,817
Derivative contracts, Liabilities	[3]	166,015		142,028
Total, Liabilities		744,305		596,845
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		10,479		38,956
Financial instruments sold, but not yet purchased, at fair value		334,630		254,265
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		158,086		73,608
Available-for-sale securities, at fair value		2,135	[1]	2,148
Financial instruments sold, but not yet purchased, at fair value		5,439		3,971
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		63,046		8,270
Available-for-sale securities, at fair value		188,677		207,725
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		321,842		202,169
Available-for-sale securities, at fair value		537,850	[1]	566,294
Financial instruments sold, but not yet purchased, at fair value		135,080		134,381
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		43,091		38,129
Investments		24,877		23,597
Financial instruments sold, but not yet purchased, at fair value		20,114		11,590
State and Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		163,139		126,237
Available-for-sale securities, at fair value		2,294	[1]	2,351
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[4]	39,396		37,136
Investments in Funds and Partnerships Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		26,098		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		199,294		172,642
Available-for-sale securities, at fair value		715,250	[1]	791,022
Financial instruments sold, but not yet purchased, at fair value		70,344		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, at fair value		65,695	[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, at fair value		332	[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		1,056,745		731,752
Financial instruments sold, but not yet purchased, at fair value		12,683	[5]	5,817	[6]
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		97,768	[7]	71,741	[8]
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		10,959		10,045
Total Assets		64,452		87,073
Financial instruments sold, but not yet purchased, at fair value		354,744		265,943
Total, Liabilities		354,744		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		10,479		38,956
Financial instruments sold, but not yet purchased, at fair value		334,630		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		197		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		42,817		37,383
Investments		10,888		9,928
Financial instruments sold, but not yet purchased, at fair value		20,114		11,590
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[4]	71		117
Level 1 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		53,493		77,028
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		1,512,233		1,636,041
Investments		2,226		1,836
Derivative contracts, Assets	[2]	166,038		142,042
Total Assets		2,593,563		2,362,576
Financial instruments sold, but not yet purchased, at fair value		217,837		183,093
Derivative contracts, Liabilities	[3]	166,015		142,028
Total, Liabilities		383,852		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		158,086		73,608
Available-for-sale securities, at fair value		2,135		2,148
Financial instruments sold, but not yet purchased, at fair value		5,439		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		61,377		6,091
Available-for-sale securities, at fair value		188,677		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		321,645		201,480
Available-for-sale securities, at fair value		537,850		566,294
Financial instruments sold, but not yet purchased, at fair value		135,080		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		274		746
Investments		2,111		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		163,139		126,237
Available-for-sale securities, at fair value		2,294		2,351
Level 2 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[4]	115		45
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		199,294		172,642
Available-for-sale securities, at fair value		715,250		791,022
Financial instruments sold, but not yet purchased, at fair value		70,344		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, at fair value		65,695		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, at fair value		332		388
Level 2 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		913,066		582,657
Financial instruments sold, but not yet purchased, at fair value		6,974	[5]	36	[6]
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		9,251	[7]	1,853	[8]
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		51,871		63,533
Total Assets		142,057		135,600
Financial instruments sold, but not yet purchased, at fair value		5,709		5,781
Total, Liabilities		5,709		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		1,669		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	[4]	39,210		36,974
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		90,186		72,067
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		88,517	[7]	69,888	[8]
Financial instruments sold, but not yet purchased, at fair value		$ 5,709	[5]	$ 5,781	[6]

[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] Primarily includes private company investments.

[5] Includes asset-backed securities and syndicated loans.

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

[7] Includes syndicated loans and non-agency mortgage-backed securities.

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