Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)		Mar. 31, 2020		Dec. 31, 2019
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 33,180,000		$ 24,937,000
Current Balance		10,123,495,000		9,727,679,000
Recorded Investment in Loans, Total		10,156,675,000		9,752,616,000
Non-Accrual		12,940,000	[1]	14,373,000	[2]
Restructured		162,000	[1]	163,000	[2]
Nonperforming loans with no allowance		1,249,000
Total	[1]	14,351,000
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		18,971,000		10,564,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		14,209,000		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		3,800,922,000		3,426,013,000
Recorded Investment in Loans, Total		3,813,862,000		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		20,050,000		11,725,000
Current Balance		3,475,086,000		3,297,823,000
Recorded Investment in Loans, Total		3,495,136,000		3,309,548,000
Non-Accrual	[2]			1,249,000
Restructured		162,000	[1]	163,000	[2]
Nonperforming loans with no allowance		1,249,000
Total	[1]	1,411,000
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		18,801,000		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		1,945,371,000		2,098,211,000
Recorded Investment in Loans, Total		1,945,371,000		2,098,211,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		146,000
Current Balance		399,586,000		428,549,000
Recorded Investment in Loans, Total		399,732,000		428,549,000
Commercial Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		146,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		412,410,000		398,839,000
Recorded Investment in Loans, Total		412,410,000		398,839,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				267,000
Current Balance		57,402,000		50,938,000
Recorded Investment in Loans, Total		57,402,000		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				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		44,000		5,000
Current Balance		32,718,000		27,306,000
Recorded Investment in Loans, Total		32,762,000		27,311,000
Other [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		24,000		$ 5,000
Other [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 20,000

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

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