Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($) $ in Thousands		Jun. 30, 2017		Dec. 31, 2016
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 1,227		$ 11,721
Current Balance		6,212,586		5,625,844
Recorded Investment in Loans, Total		6,213,813		5,637,565
Non-Accrual		5,278	[1]	17,234	[2]
Restructured		9,172	[1],[3]	9,700	[2]
Total		14,450	[1]	26,934	[2]
30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		1,041		11,523
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		186		198
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		1,035		1,923
Current Balance		2,247,493		2,159,477
Recorded Investment in Loans, Total		2,248,528		2,161,400
Restructured		174	[1],[3]	178	[2]
Total		174	[1]	178	[2]
Residential Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		1,035		1,923
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		2,064,052		1,710,399
Recorded Investment in Loans, Total		2,064,052		1,710,399
Non-Accrual		4,951	[1]	16,815	[2]
Restructured	[1],[3]	8,998
Total		13,949	[1]	16,815	[2]
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		1,755,592		1,614,033
Recorded Investment in Loans, Total		1,755,592		1,614,033
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				9,522
Current Balance		71,517		69,189
Recorded Investment in Loans, Total		71,517		78,711
Restructured	[2]			9,522
Total	[2]			9,522
Commercial Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				9,522
Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		8		2
Current Balance		42,658		45,389
Recorded Investment in Loans, Total		42,666		45,391
Non-Accrual		4	[1]	6	[2]
Total		4	[1]	6	[2]
Consumer [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		6
Consumer [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		2		2
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		184		274
Current Balance		14,119		14,734
Recorded Investment in Loans, Total		14,303		15,008
Non-Accrual		323	[1]	413	[2]
Total		323	[1]	413	[2]
Home Equity Lines Of Credit [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				78
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		196
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		17,155		12,623
Recorded Investment in Loans, Total		$ 17,155		$ 12,623

[1] There were no loans past due 90 days and still accruing interest at June 30, 2017.

[2] There were no loans past due 90 days and still accruing interest at December 31, 2016.

[3] On non-accrual status.