Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Jun. 30, 2023		Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 1,144,898		$ 731,752
Available-for-sale securities, at fair value		1,582,418		1,636,041
Investments		100,779		99,376
Cash equivalents measured at NAV		791		1,650
Derivative contracts, Assets		136,112	[1]	142,042	[2]
Total Assets		2,964,998		2,610,861
Financial instruments sold, but not yet purchased, at fair value		665,487		454,817
Derivative contracts, Liabilities		136,099	[3]	142,028	[4]
Total, Liabilities		801,586		596,845
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		24,571		38,956
Financial instruments sold, but not yet purchased, at fair value		445,251		254,265
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		351,095		73,608
Available-for-sale securities, at fair value		2,163	[5]	2,148
Financial instruments sold, but not yet purchased, at fair value		12,889		3,971
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		46,022		8,270
Available-for-sale securities, at fair value		197,472		207,725
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		243,240		202,169
Available-for-sale securities, at fair value		545,964	[5]	566,294
Financial instruments sold, but not yet purchased, at fair value		116,263		134,381
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		40,392		38,129
Investments		23,648		23,597
Financial instruments sold, but not yet purchased, at fair value		16,067		11,590
State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		159,089		126,237
Available-for-sale securities, at fair value		2,350	[5]	2,351
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		37,556	[6]	37,136	[7]
Investments in Funds and Partnerships Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		24,892		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		173,629		172,642
Available-for-sale securities, at fair value		768,548	[5]	791,022
Financial instruments sold, but not yet purchased, at fair value		69,150		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		65,578	[5]	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		343	[5]	388
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		14,683		14,681
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,144,898		731,752
Financial instruments sold, but not yet purchased, at fair value		5,867	[8]	5,817	[9]
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		106,860	[10]	71,741	[11]
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		0
Investments		10,198		10,045
Total Assets		75,302		87,073
Financial instruments sold, but not yet purchased, at fair value		461,363		265,943
Total, Liabilities		461,363		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		24,571		38,956
Financial instruments sold, but not yet purchased, at fair value		445,251		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		141		689
Financial instruments sold, but not yet purchased, at fair value		45		88
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		40,392		37,383
Investments		10,099		9,928
Financial instruments sold, but not yet purchased, at fair value		16,067		11,590
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		99	[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		65,104		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		1,582,418		1,636,041
Investments		1,786		1,836
Derivative contracts, Assets		136,112	[1]	142,042	[2]
Total Assets		2,692,590		2,362,576
Financial instruments sold, but not yet purchased, at fair value		198,257		183,093
Derivative contracts, Liabilities		136,099	[3]	142,028	[4]
Total, Liabilities		334,356		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		351,095		73,608
Available-for-sale securities, at fair value		2,163		2,148
Financial instruments sold, but not yet purchased, at fair value		12,889		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		44,043		6,091
Available-for-sale securities, at fair value		197,472		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		243,099		201,480
Available-for-sale securities, at fair value		545,964		566,294
Financial instruments sold, but not yet purchased, at fair value		116,218		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				746
Investments		1,671		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		159,089		126,237
Available-for-sale securities, at fair value		2,350		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] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		173,629		172,642
Available-for-sale securities, at fair value		768,548		791,022
Financial instruments sold, but not yet purchased, at fair value		69,150		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		65,578		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		343		388
Level 2 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		972,274		582,657
Financial instruments sold, but not yet purchased, at fair value	[9]			36
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,319	[10]	1,853	[11]
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		0
Investments		63,903		63,533
Total Assets		171,423		135,600
Financial instruments sold, but not yet purchased, at fair value		5,867		5,781
Total, Liabilities		5,867		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		1,979		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		37,342	[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		14,683		14,681
Level 3 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		107,520		72,067
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		105,541	[10]	69,888	[11]
Financial instruments sold, but not yet purchased, at fair value		$ 5,867	[8]	$ 5,781	[9]

[1] Included in other assets in the consolidated statements of financial condition.

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

[5] Due to the immaterial amount of income recognized on tax-exempt securities, yields were not calculated on a tax-equivalent basis.

[6] Primarily includes private company investments.

[7] Primarily includes private company investments.

[8] Includes syndicated loans.

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

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

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