Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)		Sep. 30, 2020		Dec. 31, 2019
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 18,422,000		$ 24,937,000
Current Balance		10,735,266,000		9,727,679,000
Recorded Investment in Loans, Total		10,753,688,000		9,752,616,000
Non-Accrual		13,084,000	[1]	14,373,000	[2]
Restructured		160,000	[1]	163,000	[2]
Nonperforming loans with no allowance	[1]	1,249,000
Total	[1]	14,493,000
Loans past due 90 days and still accruing interest		0		0
Total	[2]			14,536,000
30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		4,145,000		10,564,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		14,277,000		14,373,000
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		13,084,000		12,940,000
Current Balance		4,067,855,000		3,426,013,000
Recorded Investment in Loans, Total		4,080,939,000		3,438,953,000
Non-Accrual		13,084,000	[1]	12,940,000	[2]
Total	[1]	13,084,000
Total	[2]			12,940,000
Commercial And Industrial [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		144,000
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		12,940,000
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		4,627,000		11,725,000
Current Balance		3,800,209,000		3,297,823,000
Recorded Investment in Loans, Total		3,804,836,000		3,309,548,000
Non-Accrual	[2]			1,249,000
Restructured		160,000	[1]	163,000	[2]
Nonperforming loans with no allowance	[1]	1,249,000
Total	[1]	1,409,000
Total	[2]			1,412,000
Residential Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		3,290,000		10,476,000
Residential Real Estate [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		1,337,000		1,249,000
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		1,841,516,000		2,098,211,000
Recorded Investment in Loans, Total		1,841,516,000		2,098,211,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		386,957,000		428,549,000
Recorded Investment in Loans, Total		386,957,000		428,549,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		532,319,000		398,839,000
Recorded Investment in Loans, Total		532,319,000		398,839,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		686,000		267,000
Current Balance		66,700,000		50,938,000
Recorded Investment in Loans, Total		67,386,000		51,205,000
Non-Accrual	[2]			184,000
Total	[2]			184,000
Home Equity Lines Of Credit [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		686,000		83,000
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		25,000		5,000
Current Balance		39,710,000		27,306,000
Recorded Investment in Loans, Total		39,735,000		27,311,000
Other [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 25,000		$ 5,000

[1] There were no loans past due 90 days and still accruing interest at September 30, 2020.

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