Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 1,157,004		$ 694,028
Available-for-sale securities		2,113,893	[1]	2,230,297
Investments		117,804		113,862
Cash equivalents measured at NAV		3,004		34,192
Derivative contracts, Assets	[2]	52,129
Total Assets		3,443,834		3,072,379
Financial instruments sold, but not yet purchased, at fair value		756,150		437,978
Derivative contracts, Liabilities	[3]	52,147
Total Liabilities		808,297
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		10,774		46,900
Financial instruments sold, but not yet purchased, at fair value		377,023		91,974
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		143,793		56,450
Available-for-sale securities		1,808	[1]	4,361
Financial instruments sold, but not yet purchased, at fair value		37,395
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		132,087		3,394
Available-for-sale securities		291,054	[1]	698,133
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		255,999		194,575
Available-for-sale securities		791,893	[1]	631,758
Financial instruments sold, but not yet purchased, at fair value		153,852		162,626
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		75,056		67,593
Investments		21,308		29,496
Financial instruments sold, but not yet purchased, at fair value		28,482		30,848
State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		162,335		96,150	[4]
Available-for-sale securities		2,399	[1]	2,453
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		13,032		12,933
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		60,406		59,048
Investments in Funds and Partnerships Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		23,058		12,385
Mortgage-Backed Securities [Member] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		335,050		216,434
Available-for-sale securities		952,186	[1]	793,410
Financial instruments sold, but not yet purchased, at fair value		156,628		141,227
Mortgage-Backed Securities [Member] | Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		73,985	[1]	95,613
Mortgage-Backed Securities [Member] | Non-Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		568	[1]	4,569
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
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		41,910	[5]	12,532
Financial instruments sold, but not yet purchased, at fair value	[6]			11,303
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		84,450		114,353
Investments		24,110		39,838
Total Assets		108,560		154,191
Financial instruments sold, but not yet purchased, at fair value		405,505				$ 126,916
Total Liabilities		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		10,774		46,900
Financial instruments sold, but not yet purchased, at fair value		377,023				91,974
Level 1 [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		183		4,474
Financial instruments sold, but not yet purchased, at fair value						4,094
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		73,493		62,979
Investments		13,893		29,496
Financial instruments sold, but not yet purchased, at fair value		28,482				$ 30,848
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		10,217		10,342
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		980,766		568,391
Available-for-sale securities		2,113,893		2,230,297
Investments		16,013		6,593
Derivative contracts, Assets	[2]	52,129
Total Assets		3,162,801		2,805,281
Financial instruments sold, but not yet purchased, at fair value		350,645		311,062
Derivative contracts, Liabilities	[3]	52,147
Total Liabilities		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		143,793		56,450
Available-for-sale securities		1,808		4,361
Financial instruments sold, but not yet purchased, at fair value		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		67,381		3,385
Available-for-sale securities		291,054		698,133
Level 2 [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		255,816		190,101
Available-for-sale securities		791,893		631,758
Financial instruments sold, but not yet purchased, at fair value		153,852		158,532
Level 2 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,338		4,614
Investments		1,661
Level 2 [Member] | State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		162,335		96,150	[4]
Available-for-sale securities		2,399		2,453
Level 2 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		14,352		6,593
Level 2 [Member] | Mortgage-Backed Securities [Member] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		335,050		216,434
Available-for-sale securities		952,186		793,410
Financial instruments sold, but not yet purchased, at fair value		156,628		141,227
Level 2 [Member] | Mortgage-Backed Securities [Member] | Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		73,985		95,613
Level 2 [Member] | Mortgage-Backed Securities [Member] | Non-Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		568		4,569
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		15,053	[5]	1,257
Financial instruments sold, but not yet purchased, at fair value	[6]			11,303
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		91,788		11,284
Investments		54,623		55,046
Total Assets		146,411		66,330
Level 3 [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		64,706		9
Level 3 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		225
Investments		5,754
Level 3 [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		13,032		12,933
Level 3 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		35,837		42,113
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 26,857	[5]	$ 11,275

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

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

[6] Includes sovereign debt and state and municipal securities.