Bank Loans (Schedule of Term Loans Amortized Cost Basis by Origination Year and Revolving Cost Amortized Cost Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	$ 10,753,688	$ 9,752,616
Commercial And Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	4,080,939	3,438,953
Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	466,481
Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	105,957
Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	2,608,716
Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	32,315
Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	11,154
Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	47,790
Commercial And Industrial [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	808,526
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	3,804,836	3,309,548
Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,217,617
Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	964,320
Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	412,590
Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	327,187
Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	303,909
Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	579,213
Securities-Based Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,841,516	2,098,211
Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	21,968
Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	108,647
Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	25,825
Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	195
Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	300
Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	56,691
Securities-Based Loans [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,627,890
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	386,957	428,549
Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	74,689
Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	158,422
Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	42,576
Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	52,387
Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	14,638
Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	43,469
Commercial Real Estate [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	776
Construction And Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	532,319	398,839
Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	44,892
Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	254,524
Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	145,387
Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	68,495
Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	6,852
Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,370
Construction And Land [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	10,799
Home Equity Lines Of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	67,386	51,205
Home Equity Lines Of Credit [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	67,386
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	39,735	27,311
Other [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	6
Other [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	755
Other [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	20,049
Other [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	18,925
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	10,426,029	9,676,864
Pass [Member] | Commercial And Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	3,791,192	3,365,800
Pass [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	466,481
Pass [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	105,957
Pass [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	2,355,918
Pass [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	19,375
Pass [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	11,154
Pass [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	47,763
Pass [Member] | Commercial And Industrial [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	784,544
Pass [Member] | Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	3,802,942	3,307,719
Pass [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,217,617
Pass [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	964,320
Pass [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	412,590
Pass [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	326,393
Pass [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	303,909
Pass [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	578,113
Pass [Member] | Securities-Based Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,841,516	2,098,211
Pass [Member] | Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	21,968
Pass [Member] | Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	108,647
Pass [Member] | Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	25,825
Pass [Member] | Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	195
Pass [Member] | Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	300
Pass [Member] | Securities-Based Loans [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	56,691
Pass [Member] | Securities-Based Loans [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,627,890
Pass [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	385,645	427,963
Pass [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	74,689
Pass [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	158,422
Pass [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	42,432
Pass [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	52,387
Pass [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	13,470
Pass [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	43,469
Pass [Member] | Commercial Real Estate [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	776
Pass [Member] | Construction And Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	498,079	398,839
Pass [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	44,892
Pass [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	254,524
Pass [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	111,147
Pass [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	68,495
Pass [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	6,852
Pass [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,370
Pass [Member] | Construction And Land [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	10,799
Pass [Member] | Home Equity Lines Of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	66,920	51,021
Pass [Member] | Home Equity Lines Of Credit [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	66,920
Pass [Member] | Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	39,735	27,311
Pass [Member] | Other [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	6
Pass [Member] | Other [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	755
Pass [Member] | Other [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	20,049
Pass [Member] | Other [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	18,925
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	137,182	49,244
Special Mention [Member] | Commercial And Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	120,663	48,241
Special Mention [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	106,214
Special Mention [Member] | Commercial And Industrial [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	14,449
Special Mention [Member] | Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	645	417
Special Mention [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	645
Special Mention [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,168	586
Special Mention [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,168
Special Mention [Member] | Construction And Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	14,240
Special Mention [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	14,240
Special Mention [Member] | Home Equity Lines Of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	466
Special Mention [Member] | Home Equity Lines Of Credit [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	466
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	176,288	13,568
Substandard [Member] | Commercial And Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	156,144	11,972
Substandard [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	146,584
Substandard [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	27
Substandard [Member] | Commercial And Industrial [Member] | Revolving Loans Amortized Cost Basis [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	9,533
Substandard [Member] | Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year		1,412
Substandard [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	144
Substandard [Member] | Commercial Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	144
Substandard [Member] | Construction And Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	20,000
Substandard [Member] | Construction And Land [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	20,000
Substandard [Member] | Home Equity Lines Of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year		184
Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	14,189	12,940
Doubtful [Member] | Commercial And Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	12,940	$ 12,940
Doubtful [Member] | Commercial And Industrial [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	12,940
Doubtful [Member] | Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	1,249
Doubtful [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	149
Doubtful [Member] | Residential Real Estate [Member] | Prior [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans amortized cost basis by origination year	$ 1,100