Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($) $ in Thousands		Sep. 30, 2017		Dec. 31, 2016
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 5,787		$ 11,721
Current Balance		6,878,104		5,625,844
Recorded Investment in Loans, Total		6,883,891		5,637,565
Non-Accrual		6,074	[1]	17,234	[2]
Restructured		8,935	[1],[3]	9,700	[2]
Total		15,009	[1]	26,934	[2]
30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		5,785		11,523
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		2		198
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		5,471		1,923
Current Balance		2,512,072		2,159,477
Recorded Investment in Loans, Total		2,517,543		2,161,400
Restructured		173	[1],[3]	178	[2]
Total		173	[1]	178	[2]
Residential Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		5,471		1,923
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		2,380,417		1,710,399
Recorded Investment in Loans, Total		2,380,417		1,710,399
Non-Accrual		5,749	[1]	16,815	[2]
Restructured	[1],[3]	8,762
Total		14,511	[1]	16,815	[2]
Securities-Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		1,839,981		1,614,033
Recorded Investment in Loans, Total		1,839,981		1,614,033
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				9,522
Current Balance		78,614		69,189
Recorded Investment in Loans, Total		78,614		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		316		2
Current Balance		35,833		45,389
Recorded Investment in Loans, Total		36,149		45,391
Non-Accrual		3	[1]	6	[2]
Total		3	[1]	6	[2]
Consumer [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		314
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				274
Current Balance		13,072		14,734
Recorded Investment in Loans, Total		13,072		15,008
Non-Accrual		322	[1]	413	[2]
Total		322	[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				196
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		18,115		12,623
Recorded Investment in Loans, Total		$ 18,115		$ 12,623

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

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

[3] On non-accrual status.