Bank Loans (Risk Category Of Loan Portfolio) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	$ 6,883,891	$ 5,637,565
Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	6,840,436	5,569,259
Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	27,332	27,905
Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	16,123	40,401
Residential Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,517,543	2,161,400
Residential Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,516,586	2,161,223
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	784
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	173	177
Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,380,417	1,710,399
Commercial And Industrial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	2,338,246	1,652,211
Commercial And Industrial [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	26,548	27,905
Commercial And Industrial [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	15,623	30,283
Securities-Based Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	1,839,981	1,614,033
Securities-Based Loans [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	1,839,981	1,614,033
Commercial Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	78,614	78,711
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	78,614	69,189
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio		9,522
Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	36,149	45,391
Consumer [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	36,144	45,385
Consumer [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	5	6
Home Equity Lines Of Credit [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	13,072	15,008
Home Equity Lines Of Credit [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	12,750	14,595
Home Equity Lines Of Credit [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	322	413
Construction And Land [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	18,115	12,623
Construction And Land [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total risk category of loan portfolio	$ 18,115	$ 12,623