Fair Value Of Financial Instruments (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2025		Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	$ 1,419,156		$ 1,169,008
Available-for-sale securities	1,613,304		1,584,598
Financial instruments sold, but not yet purchased, at fair value	825,488		646,271
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,311
Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	428,765
State and Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,351
Agency Mortgage-Backed Securities [Member] | Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	991,656		921,563
Agency Mortgage-Backed Securities [Member] | Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	66,417		67,956
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	177		199
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,613,304		1,584,598
Investments	75,459		75,358
Derivative contracts, Assets	91,048	[1]	110,814	[2]
Cash equivalents measured at NAV	18,349		1,932
Total Assets	3,217,316		2,941,710
Financial instruments sold, but not yet purchased, at fair value	825,488		646,271
Derivative contracts, Liabilities	91,061	[3]	110,825	[4]
Total Liabilities	916,549		757,096
Fair Value, Recurring [Member] | U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	142,251		149,479
Available-for-sale securities	2,311		2,266
Financial instruments sold, but not yet purchased, at fair value	495,106
Fair Value, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	156,321		113,033
Available-for-sale securities	121,627		126,273
Fair Value, Recurring [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	311,548		274,207
Available-for-sale securities	428,765		463,992
Financial instruments sold, but not yet purchased, at fair value	154,125		174,425
Fair Value, Recurring [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	84,247		50,787
Investments	30,408		30,227
Financial instruments sold, but not yet purchased, at fair value	34,565		34,437
Fair Value, Recurring [Member] | State and Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	255,835		229,342
Available-for-sale securities	2,351		2,349
Fair Value, Recurring [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	552		558
Fair Value, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	13,644	[5]	14,378	[6]
Fair Value, Recurring [Member] | Investments in Funds and Partnerships Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	30,855		30,195
Fair Value, Recurring [Member] | Assets At Fair Value On Recurring Basis Before Cash Equivalents Measured at NAV [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets	3,198,967		2,939,778
Fair Value, Recurring [Member] | U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	11,963		20,045
Financial instruments sold, but not yet purchased, at fair value			370,373
Fair Value, Recurring [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	408,100		262,629
Available-for-sale securities	991,656		921,563
Financial instruments sold, but not yet purchased, at fair value	140,550		65,946
Fair Value, Recurring [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	66,417		67,956
Fair Value, Recurring [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	177		199
Sovereign Debt [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,419,156		1,169,008
Other [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	48,891	[7]	69,486	[8]
Financial instruments sold, but not yet purchased, at fair value	1,142	[9]	1,090	[10]
Level 1 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	14,914		14,691
Total Assets	110,871		85,715
Financial instruments sold, but not yet purchased, at fair value	529,671		404,810
Total Liabilities	529,671		404,810
Level 1 [Member] | Fair Value, Recurring [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	160		507
Level 1 [Member] | Fair Value, Recurring [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	83,834		50,472
Investments	14,910		14,661
Financial instruments sold, but not yet purchased, at fair value	34,565		34,437
Level 1 [Member] | Fair Value, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	4	[5]	30	[6]
Level 1 [Member] | Fair Value, Recurring [Member] | U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	11,963		20,045
Financial instruments sold, but not yet purchased, at fair value	495,106		370,373
Level 1 [Member] | Sovereign Debt [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	95,957		71,024
Level 2 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,613,304		1,584,598
Investments	1		1
Derivative contracts, Assets	91,048	[1]	110,814	[2]
Total Assets	2,974,028		2,733,896
Financial instruments sold, but not yet purchased, at fair value	294,675		240,371
Derivative contracts, Liabilities	91,061	[3]	110,825	[4]
Total Liabilities	385,736		351,196
Level 2 [Member] | Fair Value, Recurring [Member] | U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	142,251		149,479
Available-for-sale securities	2,311		2,266
Level 2 [Member] | Fair Value, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	146,156		111,999
Available-for-sale securities	121,627		126,273
Level 2 [Member] | Fair Value, Recurring [Member] | Corporate Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	311,388		273,700
Available-for-sale securities	428,765		463,992
Financial instruments sold, but not yet purchased, at fair value	154,125		174,425
Level 2 [Member] | Fair Value, Recurring [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	413		315
Investments	1		1
Level 2 [Member] | Fair Value, Recurring [Member] | State and Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	255,835		229,342
Available-for-sale securities	2,351		2,349
Level 2 [Member] | Fair Value, Recurring [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	408,100		262,629
Available-for-sale securities	991,656		921,563
Financial instruments sold, but not yet purchased, at fair value	140,550		65,946
Level 2 [Member] | Fair Value, Recurring [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	66,417		67,956
Level 2 [Member] | Fair Value, Recurring [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	177		199
Level 2 [Member] | Sovereign Debt [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,269,675		1,038,483
Level 2 [Member] | Other [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	5,532	[7]	11,019	[8]
Level 3 [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	29,689		30,471
Total Assets	83,213		89,972
Financial instruments sold, but not yet purchased, at fair value	1,142		1,090
Total Liabilities	1,142		1,090
Level 3 [Member] | Fair Value, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	10,165		1,034
Level 3 [Member] | Fair Value, Recurring [Member] | Corporate Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	15,497		15,565
Level 3 [Member] | Fair Value, Recurring [Member] | Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	552		558
Level 3 [Member] | Fair Value, Recurring [Member] | Other Investment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	13,640	[5]	14,348	[6]
Level 3 [Member] | Sovereign Debt [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	53,524		59,501
Level 3 [Member] | Other [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	43,359	[7]	58,467	[8]
Financial instruments sold, but not yet purchased, at fair value	$ 1,142	[9]	$ 1,090	[10]

[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] Primarily includes private company investments.

[6] Primarily includes private company investments.

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

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

[9] Includes syndicated loans.

[10] Includes syndicated loans