Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)		Jun. 30, 2020		Dec. 31, 2019
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 32,004,000		$ 24,937,000
Current Balance		10,542,293,000		9,727,679,000
Recorded Investment in Loans, Total		10,574,297,000		9,752,616,000
Non-Accrual		12,940,000	[1]	14,373,000	[2]
Restructured		161,000	[1]	163,000	[2]
Nonperforming loans with no allowance	[1]	1,249,000
Total	[1]	14,350,000
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		17,815,000		10,564,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		14,189,000		14,373,000
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		12,940,000		12,940,000
Current Balance		4,136,367,000		3,426,013,000
Recorded Investment in Loans, Total		4,149,307,000		3,438,953,000
Non-Accrual		12,940,000	[1]	12,940,000	[2]
Total	[1]	12,940,000
Total	[2]			12,940,000
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		18,963,000		11,725,000
Current Balance		3,691,694,000		3,297,823,000
Recorded Investment in Loans, Total		3,710,657,000		3,309,548,000
Non-Accrual	[2]			1,249,000
Restructured		161,000	[1]	163,000	[2]
Nonperforming loans with no allowance	[1]	1,249,000
Total	[1]	1,410,000
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		17,714,000		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		1,249,000		1,249,000
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		1,716,786,000		2,098,211,000
Recorded Investment in Loans, Total		1,716,786,000		2,098,211,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		406,788,000		428,549,000
Recorded Investment in Loans, Total		406,788,000		428,549,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		472,216,000		398,839,000
Recorded Investment in Loans, Total		472,216,000		398,839,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		101,000		267,000
Current Balance		62,598,000		50,938,000
Recorded Investment in Loans, Total		62,699,000		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		101,000		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				5,000
Current Balance		55,844,000		27,306,000
Recorded Investment in Loans, Total		$ 55,844,000		27,311,000
Other [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				$ 5,000

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

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