Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)		Sep. 30, 2018		Dec. 31, 2017
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 18,699,000		$ 19,961,000
Current Balance		8,325,927,000		6,994,460,000
Recorded Investment in Loans, Total		8,344,626,000		7,014,421,000
Non-Accrual		15,142,000	[1]	20,090,000	[2]
Restructured		9,105,000	[1]	9,123,000	[2]
Total		24,247,000	[1]	29,213,000	[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		3,792,000		19,961,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		14,907,000
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		3,929,000		7,892,000
Current Balance		2,788,340,000		2,585,684,000
Recorded Investment in Loans, Total		2,792,269,000		2,593,576,000
Non-Accrual	[1]	159,000
Restructured		169,000	[1]	171,000	[2]
Total		328,000	[1]	171,000	[2]
Residential Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		3,745,000		7,892,000
Residential Real Estate [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		184,000
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		14,656,000		11,883,000
Current Balance		3,112,779,000		2,426,055,000
Recorded Investment in Loans, Total		3,127,435,000		2,437,938,000
Non-Accrual		14,694,000	[1]	19,904,000	[2]
Restructured		8,936,000	[1]	8,952,000	[2]
Total		23,630,000	[1]	28,856,000	[2]
Commercial And Industrial [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				11,883,000
Commercial And Industrial [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		14,656,000
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		1,836,450,000		1,819,206,000
Recorded Investment in Loans, Total		1,836,450,000		1,819,206,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		328,814,000		116,258,000
Recorded Investment in Loans, Total		328,814,000		116,258,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		47,000		184,000
Current Balance		29,071,000		14,855,000
Recorded Investment in Loans, Total		29,118,000		15,039,000
Non-Accrual		231,000	[1]	184,000	[2]
Total		231,000	[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		47,000		184,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		120,969,000		7,896,000
Recorded Investment in Loans, Total		120,969,000		7,896,000
Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		67,000		2,000
Current Balance		109,504,000		24,506,000
Recorded Investment in Loans, Total		109,571,000		24,508,000
Non-Accrual		58,000	[1]	2,000	[2]
Total		58,000	[1]	2,000	[2]
Other [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				$ 2,000
Other [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 67,000

[1] There were no loans past due 90 days and still accruing interest at September 30, 2018.

[2] There were no loans past due 90 days and still accruing interest at December 31, 2017.