Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Sep. 30, 2022		Jun. 30, 2022		Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 997,686				$ 1,157,004
Available-for-sale securities, at fair value		1,660,847	[1]			2,113,893
Investments		101,296				117,804
Cash equivalents measured at NAV				$ 1,301		3,004
Derivative contracts, Assets	[2]					52,129
Total Assets		2,913,249				3,443,834
Financial instruments sold, but not yet purchased, at fair value		637,714				756,150
Derivative contracts, Liabilities	[3]	152,107				52,147
Total, Liabilities		789,821				808,297
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		40,140				10,774
Financial instruments sold, but not yet purchased, at fair value		378,885				377,023
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		137,765				143,793
Available-for-sale securities, at fair value		1,894	[1]			1,808
Financial instruments sold, but not yet purchased, at fair value		31,076				37,395
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		124,339				132,087
Available-for-sale securities, at fair value		218,974				291,054
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		219,271				255,999
Available-for-sale securities, at fair value		568,751	[1]			791,893
Financial instruments sold, but not yet purchased, at fair value		129,110				153,852
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		44,103				75,056
Investments		30,285				21,308
Financial instruments sold, but not yet purchased, at fair value		15,794				28,482
State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned				113,846		162,335
Available-for-sale securities, at fair value		2,314	[1]			2,399
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		34,943				60,406
Investments in Funds and Partnerships Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		21,592				23,058
Derivative contracts, Assets	[2]			152,119
Agency Mortgage-Backed Securities [Member] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		241,377				335,050
Available-for-sale securities, at fair value		801,461	[1]			952,186
Financial instruments sold, but not yet purchased, at fair value		78,025				156,628
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		66,989	[1]			73,985
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		464	[1]			568
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		14,476				13,032
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		997,686
Financial instruments sold, but not yet purchased, at fair value						2,770
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	[4]			76,845		41,910
Financial instruments sold, but not yet purchased, at fair value	[5]	4,824
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		87,834				84,450
Investments		16,444				24,110
Total Assets		104,278				108,560
Financial instruments sold, but not yet purchased, at fair value		398,169				405,505
Derivative contracts, Liabilities	[3]	0
Total, Liabilities		398,169				405,505
Level 1 [Member] | U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		40,140				10,774
Financial instruments sold, but not yet purchased, at fair value		378,885				377,023
Level 1 [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned				5,657		183
Financial instruments sold, but not yet purchased, at fair value		7,696
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		42,037				73,493
Investments		16,325				13,893
Financial instruments sold, but not yet purchased, at fair value		11,588				28,482
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		119				10,217
Level 1 [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments
Level 1 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased, at fair value	[5]	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		793,146				980,766
Available-for-sale securities, at fair value		1,660,847				2,113,893
Investments		2,127				16,013
Derivative contracts, Assets	[2]			152,119		52,129
Total Assets		2,608,239				3,162,801
Financial instruments sold, but not yet purchased, at fair value		234,721				350,645
Derivative contracts, Liabilities		152,107				52,147	[3]
Total, Liabilities		386,828				402,792
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		137,765				143,793
Available-for-sale securities, at fair value		1,894				1,808
Financial instruments sold, but not yet purchased, at fair value		31,076				37,395
Level 2 [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		79,223				67,381
Available-for-sale securities, at fair value						291,054
Level 2 [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		213,614				255,816
Available-for-sale securities, at fair value		568,751				791,893
Financial instruments sold, but not yet purchased, at fair value		121,414				153,852
Level 2 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,053				1,338
Investments		2,082				1,661
Financial instruments sold, but not yet purchased, at fair value		4,206
Level 2 [Member] | State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		113,846				162,335
Available-for-sale securities, at fair value		2,314				2,399
Level 2 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		45				14,352
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		241,377				335,050
Available-for-sale securities, at fair value		801,461				952,186
Financial instruments sold, but not yet purchased, at fair value		78,025				156,628
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		66,989				73,985
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		464				568
Level 2 [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments
Level 2 [Member] | Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased, at fair value						2,770
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned				6,268	[2]	15,053	[4]
Financial instruments sold, but not yet purchased, at fair value		0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		116,706				91,788
Investments		61,133				54,623
Derivative contracts, Assets	[2]			0
Total Assets		177,839				146,411
Financial instruments sold, but not yet purchased, at fair value		4,824
Derivative contracts, Liabilities	[3]	0
Total, Liabilities		4,824
Level 3 [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		45,116				64,706
Level 3 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,013				225
Investments		11,878				5,754
Level 3 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		34,779				35,837
Level 3 [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		14,476				13,032
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	[4]			$ 70,577		$ 26,857
Financial instruments sold, but not yet purchased, at fair value	[5]	$ 4,824

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

[5] Includes loans, state and municipal securities, and sovereign debt.