Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 116,142	$ 159,113
Current	28,904,377	28,352,199
Loans Past Due 90 Days or More Still Accruing Interest	2,148	1,964
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	75,651	129,997
Current	28,743,761	28,211,241
Loans Past Due 90 Days or More Still Accruing Interest	2,148	1,964
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	40,491	29,116
Current	160,616	140,958
Loans Past Due 90 Days or More Still Accruing Interest	0	0
30 - 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	80,324	121,143
30 - 59 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	68,762	118,300
30 - 59 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	11,562	2,843
60 - 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,258	10,914
60 - 89 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,741	9,733
60 - 89 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,517	1,181
Greater Than 90 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	28,560	27,056
Greater Than 90 Days Past Due | Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,148	1,964
Greater Than 90 Days Past Due | Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	26,412	25,092
Commercial loans | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	40,667	35,456
Current	6,147,766	6,059,672
Loans Past Due 90 Days or More Still Accruing Interest	1,945	378
Commercial loans | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	434	338
Current	1,245,841	1,233,956
Loans Past Due 90 Days or More Still Accruing Interest	0	4
Commercial loans | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	24,961	59,492
Current	14,284,752	14,054,940
Loans Past Due 90 Days or More Still Accruing Interest	1	0
Commercial loans | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,552	16,918
Current	2,522,991	2,410,091
Loans Past Due 90 Days or More Still Accruing Interest	201	19
Commercial loans | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,981	2,967
Current	1,011,487	956,285
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Commercial loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6	7,555
Current	445,402	477,442
Loans Past Due 90 Days or More Still Accruing Interest	1	1
Commercial loans | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	72,601	122,726
Current	25,658,239	25,192,386
Loans Past Due 90 Days or More Still Accruing Interest	2,148	402
Commercial loans | 30 - 59 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	34,680	28,134
Commercial loans | 30 - 59 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	379	300
Commercial loans | 30 - 59 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	24,960	59,481
Commercial loans | 30 - 59 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,711	16,082
Commercial loans | 30 - 59 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,981	2,953
Commercial loans | 30 - 59 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1	7,391
Commercial loans | 30 - 59 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	65,712	114,341
Commercial loans | 60 - 89 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,042	6,944
Commercial loans | 60 - 89 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	55	34
Commercial loans | 60 - 89 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	11
Commercial loans | 60 - 89 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	640	817
Commercial loans | 60 - 89 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	14
Commercial loans | 60 - 89 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4	163
Commercial loans | 60 - 89 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,741	7,983
Commercial loans | Greater Than 90 Days Past Due | Software/internet
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,945	378
Commercial loans | Greater Than 90 Days Past Due | Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	4
Commercial loans | Greater Than 90 Days Past Due | Private equity/venture capital
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1	0
Commercial loans | Greater Than 90 Days Past Due | Life science/healthcare
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	201	19
Commercial loans | Greater Than 90 Days Past Due | Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial loans | Greater Than 90 Days Past Due | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1	1
Commercial loans | Greater Than 90 Days Past Due | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,148	402
Consumer loans | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,050	6,910
Current	2,664,875	2,598,496
Loans Past Due 90 Days or More Still Accruing Interest	0	1,562
Consumer loans | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	361
Current	420,647	420,359
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,050	7,271
Current	3,085,522	3,018,855
Loans Past Due 90 Days or More Still Accruing Interest	0	1,562
Consumer loans | 30 - 59 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,050	3,598
Consumer loans | 30 - 59 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	361
Consumer loans | 30 - 59 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,050	3,959
Consumer loans | 60 - 89 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,750
Consumer loans | 60 - 89 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer loans | 60 - 89 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,750
Consumer loans | Greater Than 90 Days Past Due | Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	1,562
Consumer loans | Greater Than 90 Days Past Due | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Consumer loans | Greater Than 90 Days Past Due | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 1,562