Bank Loans (Risk Category Of Loan Portfolio) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	$ 7,425,423	$ 7,014,421
Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	7,353,703	6,960,969
Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	47,636	22,752
Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	24,084	30,700
Residential Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,703,935	2,593,576
Residential Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,703,765	2,593,096
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio		309
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	170	171
Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,677,096	2,437,938
Commercial And Industrial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,605,740	2,385,152
Commercial And Industrial [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	47,636	22,443
Commercial And Industrial [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	23,720	30,343
Securities-Based Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	1,845,592	1,819,206
Securities-Based Loans [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	1,845,592	1,819,206
Commercial Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	127,253	116,258
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	127,253	116,258
Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	24,392	24,508
Consumer [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	24,391	24,506
Consumer [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	1	2
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	21,730	15,039
Home Equity Lines Of Credit [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	21,537	14,855
Home Equity Lines Of Credit [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	193	184
Construction And Land [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	25,425	7,896
Construction And Land [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	$ 25,425	$ 7,896