Bank Loans (Aging Of The Recorded Investment In Past Due Loans) (Details) - USD ($)		Sep. 30, 2016		Dec. 31, 2015		Sep. 30, 2015
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 3,153,000		$ 4,116,000
Current Balance		4,993,891,000		3,176,468,000
Recorded Investment in Loans, Total		4,997,044,000		3,180,584,000		$ 2,442,343,000
Non-Accrual		28,161,000	[1]	737,000	[2]
Restructured		140,000	[1]	326,000	[2]
Total		28,301,000	[1]	1,063,000	[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		2,913,000		3,640,000
90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		240,000		476,000
Commercial And Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		1,558,284,000		1,216,656,000
Recorded Investment in Loans, Total		1,558,284,000		1,216,656,000		1,121,643,000
Non-Accrual	[1]	17,938,000
Total	[1]	17,938,000
Securities Based Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		1,452,913,000		1,388,953,000
Recorded Investment in Loans, Total		1,452,913,000		1,388,953,000		1,004,142,000
Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		4,000		14,000
Current Balance		92,570,000		36,832,000
Recorded Investment in Loans, Total		92,574,000		36,846,000		22,055,000
Non-Accrual		9,000	[1]	15,000	[2]
Total		9,000	[1]	15,000	[2]
Consumer [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		2,000		7,000
Consumer [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		2,000		7,000
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		2,954,000		3,760,000
Current Balance		1,801,158,000		425,372,000
Recorded Investment in Loans, Total		1,804,112,000		429,132,000		260,958,000
Non-Accrual		369,000	[1]	380,000	[2]
Restructured		140,000	[1]	326,000	[2]
Total		509,000	[1]	706,000	[2]
Residential Real Estate [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		2,716,000		3,310,000
Residential Real Estate [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		238,000		450,000
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		63,680,000		92,623,000
Recorded Investment in Loans, Total		63,680,000		92,623,000		19,811,000
Non-Accrual	[1]	9,522,000
Total	[1]	9,522,000
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		195,000		342,000
Current Balance		14,219,000		12,133,000
Recorded Investment in Loans, Total		14,414,000		12,475,000		11,260,000
Non-Accrual		323,000	[1]	342,000	[2]
Total		323,000	[1]	342,000	[2]
Home Equity Lines Of Credit [Member] | 30 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		195,000		323,000
Home Equity Lines Of Credit [Member] | 90 or More Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due				19,000
Construction And Land [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Current Balance		11,067,000		3,899,000
Recorded Investment in Loans, Total		$ 11,067,000		$ 3,899,000		$ 2,474,000

[1] There were no loans past due 90 days and still accruing interest at September 30, 2016.

[2] There were no loans past due 90 days and still accruing interest at December 31, 2015.