Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)	Jun. 30, 2018		Dec. 31, 2017
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 17,662,000		$ 19,961,000
Current Balance	7,407,761,000		6,994,460,000
Recorded Investment in Loans, Total	7,425,423,000		7,014,421,000
Non-Accrual	14,977,000	[1]	20,090,000	[2]
Restructured	9,107,000	[1]	9,123,000	[2]
Total	24,084,000	[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	3,143,000		19,961,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	14,519,000
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,811,000		7,892,000
Current Balance	2,701,124,000		2,585,684,000
Recorded Investment in Loans, Total	2,703,935,000		2,593,576,000
Restructured	170,000	[1]	171,000	[2]
Total	170,000	[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	2,811,000		7,892,000
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	14,510,000		11,883,000
Current Balance	2,662,586,000		2,426,055,000
Recorded Investment in Loans, Total	2,677,096,000		2,437,938,000
Non-Accrual	14,783,000	[1]	19,904,000	[2]
Restructured	8,937,000	[1]	8,952,000	[2]
Total	23,720,000	[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	14,510,000
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance	1,845,592,000		1,819,206,000
Recorded Investment in Loans, Total	1,845,592,000		1,819,206,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance	127,253,000		116,258,000
Recorded Investment in Loans, Total	127,253,000		116,258,000
Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due			2,000
Current Balance	24,392,000		24,506,000
Recorded Investment in Loans, Total	24,392,000		24,508,000
Non-Accrual	1,000	[1]	2,000	[2]
Total	1,000	[1]	2,000	[2]
Consumer [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due			2,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	341,000		184,000
Current Balance	21,389,000		14,855,000
Recorded Investment in Loans, Total	21,730,000		15,039,000
Non-Accrual	193,000	[1]	184,000	[2]
Total	193,000	[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	332,000		184,000
Home Equity Lines Of Credit [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	9,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance	25,425,000		7,896,000
Recorded Investment in Loans, Total	$ 25,425,000		$ 7,896,000

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

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