Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)	Mar. 31, 2019		Dec. 31, 2018
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 20,925,000		$ 22,170,000
Current Balance	8,788,159,000		8,559,477,000
Recorded Investment in Loans, Total	8,809,084,000		8,581,647,000
Non-accrual	15,550,000	[1]	15,298,000	[2]
Restructured	9,103,000	[1]	9,103,000	[2]
Total	24,653,000	[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	5,989,000		7,003,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	14,936,000		15,167,000
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	14,644,000		14,656,000
Current Balance	3,299,920,000		3,289,578,000
Recorded Investment in Loans, Total	3,314,564,000		3,304,234,000
Non-accrual	14,718,000	[1]	14,741,000	[2]
Restructured	8,936,000	[1]	8,936,000	[2]
Total	23,654,000	[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	14,644,000		14,656,000
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	6,171,000		7,347,000
Current Balance	2,922,057,000		2,867,667,000
Recorded Investment in Loans, Total	2,928,228,000		2,875,014,000
Non-accrual	452,000	[1]	352,000	[2]
Restructured	167,000	[1]	167,000	[2]
Total	619,000	[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	5,944,000		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	227,000		377,000
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance	1,860,989,000		1,786,966,000
Recorded Investment in Loans, Total	1,860,989,000		1,786,966,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance	361,950,000		318,961,000
Recorded Investment in Loans, Total	361,950,000		318,961,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance	175,023,000		138,245,000
Recorded Investment in Loans, Total	175,023,000		138,245,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due			33,000
Current Balance	44,235,000		38,065,000
Recorded Investment in Loans, Total	44,235,000		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			33,000
Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	110,000		134,000
Current Balance	123,985,000		119,995,000
Recorded Investment in Loans, Total	124,095,000		120,129,000
Non-accrual	196,000	[1]	21,000	[2]
Total	196,000	[1]	21,000	[2]
Other [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	45,000
Other [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 65,000		$ 134,000

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

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