Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands		Mar. 31, 2022		Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 1,279,636		$ 1,157,004
Available-for-sale securities		1,926,144	[1]	2,113,893
Investments		113,302		117,804
Cash equivalents measured at NAV		3,383		3,004
Derivative contracts, Assets	[2]			52,129
Total Assets		3,397,111		3,443,834
Financial instruments sold, but not yet purchased, at fair value		941,415		756,150
Derivative contracts, Liabilities		74,658	[3]	52,147	[4]
Total, Liabilities		1,016,073		808,297
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		60,821		10,774
Financial instruments sold, but not yet purchased, at fair value		481,889		377,023
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		210,855		143,793
Available-for-sale securities		2,922	[1]	1,808
Financial instruments sold, but not yet purchased, at fair value		69,181		37,395
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		72,990		132,087
Available-for-sale securities		265,680		291,054
Investments		27,269
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		258,717		255,999
Available-for-sale securities		730,874	[1]	791,893
Financial instruments sold, but not yet purchased, at fair value		198,815		153,852
Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		73,050		75,056
Investments				21,308
Financial instruments sold, but not yet purchased, at fair value		22,485		28,482
State And Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		202,737		162,335
Available-for-sale securities		2,366	[1]	2,399
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		13,743		13,032
Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		48,707		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		23,583		23,058
Derivative contracts, Assets	[5]	74,646
Agency Mortgage-Backed Securities [Member] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		348,695		335,050
Available-for-sale securities		853,946	[1]	952,186
Financial instruments sold, but not yet purchased, at fair value		164,838		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		69,852	[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		504	[1]	568
Sovereign Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,279,636
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		51,771	[6]	41,910	[7]
Financial instruments sold, but not yet purchased, at fair value	[8]	4,207
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		133,240		84,450
Investments		13,857		24,110
Total Assets		147,097		108,560
Financial instruments sold, but not yet purchased, at fair value		504,870		405,505
Total, Liabilities		504,870		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		60,821		10,774
Financial instruments sold, but not yet purchased, at fair value		481,889		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		1,529		183
Financial instruments sold, but not yet purchased, at fair value		496
Level 1 [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		70,890		73,493
Investments		13,730		13,893
Financial instruments sold, but not yet purchased, at fair value		22,485		28,482
Level 1 [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments				0
Level 1 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments				10,217
Level 1 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		127
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		1,057,007		980,766
Available-for-sale securities		1,926,144		2,113,893
Investments		15,516		16,013
Derivative contracts, Assets		74,646	[5]	52,129	[2]
Total Assets		3,073,313		3,162,801
Financial instruments sold, but not yet purchased, at fair value		436,545		350,645
Derivative contracts, Liabilities		74,658	[3]	52,147	[4]
Total, Liabilities		511,203		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		210,855		143,793
Available-for-sale securities		2,922		1,808
Financial instruments sold, but not yet purchased, at fair value		69,181		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		19,574		67,381
Available-for-sale securities				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		257,188		255,816
Available-for-sale securities		730,874		791,893
Financial instruments sold, but not yet purchased, at fair value		198,319		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		1,147		1,338
Investments		1,661		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		202,737		162,335
Available-for-sale securities		2,366		2,399
Level 2 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments				0
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		348,695		335,050
Available-for-sale securities		853,946		952,186
Financial instruments sold, but not yet purchased, at fair value		164,838		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		69,852		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		504		568
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		16,811	[6]	15,053	[7]
Investments		13,855		14,352
Financial instruments sold, but not yet purchased, at fair value	[8]	4,207
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		89,389		91,788
Investments		60,346		54,623
Total Assets		149,735		146,411
Level 3 [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		53,416		64,706
Level 3 [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		0
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] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		13,743		13,032
Level 3 [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		34,725
Level 3 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned		$ 34,960	[6]	26,857	[7]
Investments				$ 35,837

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

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

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

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

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