Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Jun. 30, 2022		Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 1,271,032		$ 1,157,004
Available-for-sale securities, at fair value		1,879,904	[1]	2,113,893
Investments		96,519		117,804
Cash equivalents measured at NAV		3,189		3,004
Derivative contracts, Assets	[2]			52,129
Total Assets		3,352,892		3,443,834
Financial instruments sold, but not yet purchased, at fair value		811,902		756,150
Derivative contracts, Liabilities	[3]	102,247		52,147
Total, Liabilities		914,149		808,297
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		55,870		10,774
Financial instruments sold, but not yet purchased, at fair value		478,722		377,023
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		201,613		143,793
Available-for-sale securities, at fair value		2,272	[1]	1,808
Financial instruments sold, but not yet purchased, at fair value		56,721		37,395
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		128,314		132,087
Available-for-sale securities, at fair value		243,588		291,054
Investments		24,949
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		230,175		255,999
Available-for-sale securities, at fair value		686,906	[1]	791,893
Financial instruments sold, but not yet purchased, at fair value		124,305		153,852
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		56,622		75,056
Investments				21,308
Financial instruments sold, but not yet purchased, at fair value		25,034		28,482
State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		136,879		162,335
Available-for-sale securities, at fair value		2,355	[1]	2,399
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		34,919		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		22,686		23,058
Derivative contracts, Assets	[2]	102,248
Agency Mortgage-Backed Securities [Member] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		349,887		335,050
Available-for-sale securities, at fair value		875,784	[1]	952,186
Financial instruments sold, but not yet purchased, at fair value		122,369		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		68,512	[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		487	[1]	568
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		13,965		13,032
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,271,032
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]	111,672		41,910
Financial instruments sold, but not yet purchased, at fair value	[5]	4,751
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		109,401		84,450
Investments		11,505		24,110
Total Assets		120,906		108,560
Financial instruments sold, but not yet purchased, at fair value		501,598		405,505
Derivative contracts, Liabilities	[3]	0
Total, Liabilities		501,598		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		55,870		10,774
Financial instruments sold, but not yet purchased, at fair value		478,722		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		1,639		183
Financial instruments sold, but not yet purchased, at fair value		63
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		51,892		73,493
Investments		11,410		13,893
Financial instruments sold, but not yet purchased, at fair value		22,813		28,482
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		95		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		1,015,220		980,766
Available-for-sale securities, at fair value		1,879,904		2,113,893
Investments		1,706		16,013
Derivative contracts, Assets	[2]	102,248		52,129
Total Assets		2,999,078		3,162,801
Financial instruments sold, but not yet purchased, at fair value		307,182		350,645
Derivative contracts, Liabilities		102,247		52,147	[3]
Total, Liabilities		409,429		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		201,613		143,793
Available-for-sale securities, at fair value		2,272		1,808
Financial instruments sold, but not yet purchased, at fair value		56,721		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		83,103		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		228,536		255,816
Available-for-sale securities, at fair value		686,906		791,893
Financial instruments sold, but not yet purchased, at fair value		124,242		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		3,717		1,338
Investments		1,661		1,661
Financial instruments sold, but not yet purchased, at fair value		2,221
Level 2 [Member] | State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		136,879		162,335
Available-for-sale securities, at fair value		2,355		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		349,887		335,050
Available-for-sale securities, at fair value		875,784		952,186
Financial instruments sold, but not yet purchased, at fair value		122,369		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		68,512		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		487		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		11,485	[2]	15,053	[4]
Financial instruments sold, but not yet purchased, at fair value		1,629
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		146,411		91,788
Investments		60,622		54,623
Derivative contracts, Assets	[2]	0
Total Assets		207,033		146,411
Financial instruments sold, but not yet purchased, at fair value		3,122
Derivative contracts, Liabilities	[3]	0
Total, Liabilities		3,122
Level 3 [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		45,211		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		13,965		13,032
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	[4]	100,187		$ 26,857
Financial instruments sold, but not yet purchased, at fair value	[5]	$ 3,122

[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.