Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)		Dec. 31, 2019		Dec. 31, 2018
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 24,937,000		$ 22,170,000
Current Balance		9,727,679,000		8,559,477,000
Recorded Investment in Loans, Total		9,752,616,000		8,581,647,000
Non-accrual		14,373,000	[1]	15,298,000	[2]
Restructured		163,000	[1]	9,103,000	[2]
Total		14,536,000	[1]	24,401,000	[2]
Loans past due 90 days and still accruing interest		0		0
30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		10,564,000		7,003,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		14,373,000		15,167,000
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		12,940,000		14,656,000
Current Balance		3,426,013,000		3,289,578,000
Recorded Investment in Loans, Total		3,438,953,000		3,304,234,000
Non-accrual		12,940,000	[1]	14,741,000	[2]
Restructured	[2]			8,936,000
Total		12,940,000	[1]	23,677,000	[2]
Commercial And Industrial [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		12,940,000		14,656,000
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		11,725,000		7,347,000
Current Balance		3,297,823,000		2,867,667,000
Recorded Investment in Loans, Total		3,309,548,000		2,875,014,000
Non-accrual		1,249,000	[1]	352,000	[2]
Restructured		163,000	[1]	167,000	[2]
Total		1,412,000	[1]	519,000	[2]
Residential Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		10,476,000		6,970,000
Residential Real Estate [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		1,249,000		377,000
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		2,098,211,000		1,786,966,000
Recorded Investment in Loans, Total		2,098,211,000		1,786,966,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		428,549,000		318,961,000
Recorded Investment in Loans, Total		428,549,000		318,961,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		398,839,000		138,245,000
Recorded Investment in Loans, Total		398,839,000		138,245,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		267,000		33,000
Current Balance		50,938,000		38,065,000
Recorded Investment in Loans, Total		51,205,000		38,098,000
Non-accrual		184,000	[1]	184,000	[2]
Total		184,000	[1]	184,000	[2]
Home Equity Lines Of Credit [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		83,000		33,000
Home Equity Lines Of Credit [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		184,000
Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		5,000		134,000
Current Balance		27,306,000		119,995,000
Recorded Investment in Loans, Total		27,311,000		120,129,000
Non-accrual	[2]			21,000
Total	[2]			21,000
Other [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 5,000
Other [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				$ 134,000

[1] There were no loans past due 90 days and still accruing interest at December 31, 2019.

[2] There were no loans past due 90 days and still accruing interest at December 31, 2018.