Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)		Mar. 31, 2021		Dec. 31, 2020
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 17,668,000		$ 18,241,000
Current Balance		12,197,524,000		11,152,572,000
Total		12,215,192,000		11,170,813,000
Non-Accrual		12,228,000	[1]	12,395,000
Restructured		158,000	[1]	158,000	[2]
Nonperforming loans with no allowance		1,249,000	[1]	1,249,000	[2]
Total		13,635,000	[1]	13,802,000	[2]
Loans past due 90 days and still accruing interest		0		0
Non-Accrual		12,228,000	[1]	12,395,000
Commercial And Industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		11,408,000		12,251,000
Current Balance		4,912,086,000		4,283,838,000
Total		4,923,494,000		4,296,089,000
Non-Accrual		11,408,000	[1]	12,251,000
Total		11,408,000	[1]	12,251,000	[2]
Non-Accrual		11,408,000	[1]	12,251,000
Residential Mortgage
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		5,866,000		5,803,000
Current Balance		4,152,167,000		3,950,867,000
Total		4,158,033,000		3,956,670,000
Non-Accrual	[1]	676,000
Restructured		158,000	[1]	158,000	[2]
Nonperforming loans with no allowance		1,249,000	[1]	1,249,000	[2]
Total		2,083,000	[1]	1,407,000	[2]
Non-Accrual	[1]	676,000
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		2,089,747,000		1,933,974,000
Total		2,089,747,000		1,933,974,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		144,000		144,000
Current Balance		374,592,000		366,341,000
Total		374,736,000		366,485,000
Non-Accrual		144,000	[1]	144,000
Total		144,000	[1]	144,000	[2]
Non-Accrual		144,000	[1]	144,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		560,191,000		501,681,000
Total		560,191,000		501,681,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		233,000		12,000
Current Balance		70,939,000		75,495,000
Total		71,172,000		75,507,000
Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		17,000		31,000
Current Balance		37,802,000		40,376,000
Total		37,819,000		40,407,000
30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		4,191,000		4,611,000
30 - 89 Days Past Due [Member] | Commercial And Industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				14,000
30 - 89 Days Past Due [Member] | Residential Mortgage
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		3,941,000		4,554,000
30 - 89 Days Past Due [Member] | Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		233,000		12,000
30 - 89 Days Past Due [Member] | Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		17,000		31,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		13,477,000		13,630,000
90 or More Days Past Due [Member] | Commercial And Industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		11,408,000		12,237,000
90 or More Days Past Due [Member] | Residential Mortgage
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		1,925,000		1,249,000
90 or More Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 144,000		$ 144,000

[1] There were no loans past due 90 days and still accruing interest at March 31, 2021.

[2] There were no loans past due 90 days and still accruing interest at December 31, 2020.